Practical Cladding Repair Cases for Engineering Machinery Parts

Literature Overview

This study, authored by Wan Weiguo from Maanshan Iron and Steel Co., Ltd., was published in the journal Construction Machinery in 2000. The paper presents a series of practical case studies of weld overlay repair on engineering machinery parts, including excavator buckets, bulldozer blades, scraper buckets, and conveyor rollers. These components are subject to severe abrasive wear from contact with soil, rock, and ore, and their timely repair through weld overlay is essential for maintaining the availability and productivity of the machinery. The paper provides valuable practical insights into the selection of welding consumables, process parameters, and repair procedures for different types of wear-damaged components.

Technical Background

Engineering machinery parts are typically fabricated from low-carbon or low-alloy steels such as Q235, Q345, or 16Mn. These materials possess adequate strength and toughness but insufficient wear resistance for the abrasive conditions encountered in construction and mining operations. When the wear allowance on these components is exceeded, they must be repaired by applying a hardfacing overlay that restores the dimensional tolerance and provides enhanced wear resistance. The most common hardfacing alloys used for this purpose are:

Hardfacing Alloy	Composition (approx.)	Hardness (HV)	Application
High-carbon martensitic	C 2.5–4.0, Cr 5–10	600–800	Excavator buckets, bulldozer blades
Carbide-forming (Cr-based)	Cr 20–30, C 2–3	800–1000	Scraper buckets, conveyor rollers
Nickel-based (Stellite)	Co 60, Cr 25, W 5	400–500	High-temperature wear parts
Cast iron (nodular)	C 3.0–3.5, Si 2.0–3.0	200–400	Wear plates, gudgeon pins

Case Study 1: Excavator Bucket Edge Repair

The first case involves the repair of an excavator bucket edge that has been worn down by 25 mm due to contact with hard rock. The repair procedure is as follows:

Surface preparation: The worn surface is ground to remove the decarburized and contaminated layer, exposing a clean base metal surface.
Preheat: The component is preheated to 150–200 °C using a gas torch to reduce the cooling rate and prevent cracking.
Welding consumable: A high-carbon martensitic hardfacing electrode (e.g., D256 or equivalent) is used. The electrode diameter is 4.0 mm, and the welding current is 180–220 A.
Welding procedure: Two passes are applied. The first pass is applied with a low current (150 A) to minimize dilution from the base metal. The second pass is applied with a higher current (200 A) to build up the required thickness.
Post-weld treatment: The weld is air-cooled to promote the formation of hard martensite in the weld metal. No PWHT is applied, as this would reduce the hardness of the martensitic structure.
Result: The overlay hardness is 700–750 HV, and the service life is extended by approximately 18 months.

Case Study 2: Bulldozer Blade Wear Plate Repair

The second case involves the repair of a bulldozer blade wear plate that has been worn through by contact with abrasive soil. The repair procedure is as follows:

Surface preparation: The worn area is ground to a depth of 3 mm to remove the contaminated surface.
Preheat: The component is preheated to 200 °C to prevent cracking of the low-carbon steel substrate.
Welding consumable: A chromium-based carbide-forming hardfacing electrode (e.g., D307 or equivalent) is used. The electrode diameter is 3.2 mm, and the welding current is 120–160 A.
Welding procedure: Three passes are applied in a staggered pattern to ensure uniform coverage. The interpass temperature is maintained below 250 °C.
Post-weld treatment: The weld is air-cooled. No PWHT is applied.
Result: The overlay hardness is 850–900 HV, and the service life is extended by approximately 24 months.

Case Study 3: Conveyor Roller Surface Repair

The third case involves the repair of a conveyor roller surface that has been worn by contact with abrasive material. The repair procedure is as follows:

Surface preparation: The worn surface is ground to remove the decarburized layer.
Preheat: The roller is preheated to 100–150 °C using an induction heater.
Welding consumable: A submerged arc welding (SAW) process with low-hydrogen flux and a hardfacing wire (e.g., H08Mn2SiA) is used.
Welding procedure: Two passes are applied with a travel speed of 300 mm/min and a welding current of 400 A.
Post-weld treatment: The weld is air-cooled.
Result: The overlay hardness is 600–650 HV, and the service life is extended by approximately 12 months.

Common Defects and Countermeasures

The following defects are commonly encountered in the repair of engineering machinery parts:

Defect	Cause	Countermeasure
Cracking	High cooling rate, hydrogen pickup, stress concentration	Increase preheat, use low-hydrogen consumables, apply PWHT if required
Porosity	Moisture in consumables, contaminated surface	Dry consumables, clean surface, use inert gas shielding
Poor adhesion	Insufficient heat input, surface contamination	Increase preheat, grind surface, increase current
Undercut	Excessive travel speed, incorrect electrode angle	Reduce travel speed, correct electrode angle
Excessive dilution	High heat input, large electrode diameter	Reduce current, use smaller electrode, apply first pass with low heat input

Study Insights and Implications

This paper provides a practical guide for the repair of engineering machinery parts through weld overlay. The case studies demonstrate that the successful repair of these components requires a careful selection of welding consumables, process parameters, and post-weld treatment procedures based on the specific wear conditions and service requirements. The emphasis on surface preparation and preheat is particularly important, as these are often neglected in field repair operations. The paper also highlights the importance of matching the overlay hardness to the service conditions: too hard an overlay may be brittle and prone to spalling, while too soft an overlay may not provide adequate wear resistance. For maintenance engineers and field welders, this paper serves as a practical reference for the selection of repair procedures and consumables for common engineering machinery components.