Research on Grey Cast Iron Surfacing Process

Literature Overview

This paper by Liu Cheng, Li Jiangong, and Liu Huipeng, published in Hot Working Technology (2013, Vol. 42, No. 9, pp. 189-191), presents a practical multi-layer surfacing approach for repairing a worn winch drum made of HT200 grey cast iron. Funded by the Hebei Provincial Department of Education Research Project (Z2011296), the study developed and evaluated custom flux-cored wires for each surfacing layer, demonstrating excellent field performance after repair.

Multi-Layer Surfacing Strategy

The repair approach employs a three-layer strategy, each layer designed for a specific metallurgical function:

Layer	Function	Filler Wire Type	Key Composition Features
Base layer (underlay)	Fusion and ductility	High Mn, high Si alloy steel FCAW	Enhanced wetting and fusion with grey iron
Transition layer	Stress relief and property gradient	Low carbon, low chromium FCAW	Moderate hardness, good toughness
Wear layer (overlay)	Wear resistance	High carbon, high chromium cast iron FCAW	Hard carbide formation, high hardness

This layered approach addresses the fundamental challenge of grey cast iron surfacing: the need to achieve both good fusion with the brittle grey iron substrate and high wear resistance in the final surface layer. A single-layer approach cannot simultaneously satisfy both requirements.

Welding Process Parameters

The surfacing was performed using CO₂ gas shielded flux-cored wire welding (FCAW-C):

Shielding gas: CO₂
Welding current: 200-300 A (depending on wire diameter)
Voltage: 22-28 V
Travel speed: Optimized for each layer
Preheating: 200-300°C to minimize cracking
Interpass temperature: Controlled to prevent excessive hardness in base layer

The CO₂ shielding provides good penetration and arc stability while being economical for field repair applications. The flux-cored wire format allows precise control of alloy composition through the flux core, enabling the tailored properties required for each layer.

Microstructural and Performance Analysis

Six specimens were prepared by combining the three wire types in different configurations:

Specimen	Base Layer	Transition Layer	Overlay Layer	Hardness (HRC)	Wear Resistance
Combination 1	High Mn-Si	Low C-Cr	High C-Cr	55-60	Good
Combination 2	High Mn-Si	Low C-Cr	High C-Cr	58-62	Excellent
Other combinations	Various	Various	Various	Variable	Variable

The optimal combination was determined through metallographic examination, hardness profiling, and pin-on-disk wear testing. The best results were achieved with the high Mn-Si base layer providing excellent fusion, followed by a low C-Cr transition layer that gradually increases hardness, and finally a high C-Cr overlay that forms hard cementite and chromium carbide networks for maximum wear resistance.

Metallurgical Analysis

The high Mn-Si base layer achieves good fusion with grey cast iron through several mechanisms:

Silicon promotes wetting: Silicon reduces surface tension at the interface, improving molten metal flow and fusion with the graphite-containing base metal.
Manganese acts as deoxidizer: Prevents oxide formation at the interface and promotes clean fusion.
Rapid solidification: The base layer solidifies quickly, limiting carbon diffusion from the grey iron and minimizing white cast iron formation.

The high C-Cr overlay achieves wear resistance through:

Hard carbide formation: Carbon and chromium form M₇C₃ and M₃C carbides with hardness exceeding 1000 HV
Martensitic matrix: The high carbon content promotes martensite formation upon solidification
Carbide network: A continuous network of hard carbides in a tough matrix provides excellent wear resistance

Engineering Practice and Field Results

The repaired winch drum demonstrated excellent performance in field service, validating the multi-layer surfacing approach. Key practical considerations include:

Preparation: The worn surface must be thoroughly cleaned and profiled to remove old coatings and provide adequate material for fusion
Preheating: Essential for grey iron to prevent cracking, particularly in thick sections
Layer thickness: Each layer should be deposited in thin passes (2-3 mm) to minimize thermal stresses
Final machining: The overlay may require machining to achieve dimensional tolerances, with adequate overlay thickness to accommodate machining allowance

This work demonstrates that even with relatively simple equipment (CO₂ FCAW), proper material selection and process design can achieve excellent repair results for grey cast iron components. The custom flux-cored wire approach offers advantages over commercially available surfacing electrodes in terms of composition flexibility and cost-effectiveness. For industrial maintenance operations dealing with worn grey iron components—cranes, winches, pumps, and machinery bases—this multi-layer approach provides a reliable and economical repair methodology.