Effect of Different Cooling Methods on Mechanical Properties of Wear-Resistant Overlay Plates

Literature Overview

This study, published in 2013 by Wang Liyue, Han Bingyin, and Wang Xiaoping from Anhui Institute of Mechanical and Electrical Engineering and Anhui Conch Kawasaki Energy-Saving Equipment Manufacturing Co., Ltd., investigates the influence of various cooling methods on the mechanical properties of wear-resistant weld overlay plates. The research falls under the category of thermal processing technology and addresses a practical challenge encountered in the manufacturing of wear-resistant equipment components where overlay welding is applied to extend service life. The authors examined how different post-weld cooling regimes—ranging from air cooling to controlled furnace cooling and water quenching—affect hardness, tensile strength, impact toughness, and microstructural evolution in the overlay layer and its heat-affected zone.

Core Technical Findings

The fundamental principle behind this investigation is that the cooling rate following overlay welding directly controls the phase transformation behavior in the deposited material. For high-carbon and high-alloy wear-resistant overlay systems, the cooling rate determines whether martensite, bainite, or retained austenite forms as the dominant phase, each contributing differently to hardness and toughness characteristics.

The study compared several cooling methods including free air cooling, accelerated air cooling, furnace cooling at controlled rates, and water quenching. The results demonstrated that slower cooling rates generally produced lower hardness values but improved impact toughness, while faster cooling rates increased hardness at the expense of toughness and increased susceptibility to cracking. The hardness gradient across the overlay layer was found to be non-uniform, with the surface layers exhibiting higher hardness due to faster local cooling rates compared to the deeper layers closer to the base metal interface.

Technical Parameter Analysis

The microstructural analysis revealed that water quenching produced predominantly martensitic structures with high carbon content in solution, resulting in peak hardness values exceeding 700 HV in some cases. However, the rapid transformation created significant residual stresses that promoted crack initiation at the overlay-base metal interface. Free air cooling allowed partial austenite decomposition to bainite, producing a more balanced combination of hardness and ductility. Furnace cooling at rates below 2 °C/s promoted complete austenite decomposition to pearlite and ferrite, significantly reducing hardness but maximizing toughness.

Engineering Practice Implications

From a practical standpoint, this research provides critical guidance for selecting appropriate cooling methods based on the specific service conditions of wear-resistant components. For applications requiring maximum wear resistance such as crusher cones, grinding balls, and excavator bucket teeth, water quenching or accelerated air cooling may be acceptable provided that the overlay material has low cracking susceptibility and the component geometry does not create excessive stress concentrations. For thicker overlay deposits or components operating under cyclic loading conditions, furnace cooling or controlled air cooling is strongly recommended to prevent delayed cracking.

The study also highlights the importance of understanding the hardness gradient within the overlay layer. In many industrial applications, the surface hardness is more critical for wear resistance while the subsurface toughness determines resistance to spalling and delamination. The non-uniform cooling profile inherent to multi-pass overlay welding naturally creates this gradient, but the final cooling method can either enhance or diminish this beneficial distribution.

Key Reflections and Insights

One of the most valuable contributions of this work is the systematic comparison of cooling methods under otherwise identical welding parameters. In industrial practice, cooling methods are often selected based on empirical experience rather than systematic evaluation. The authors demonstrated that the optimal cooling method depends on the specific overlay alloy system, the thickness of the deposit, and the component geometry. For thin overlay layers less than 3 mm thick, air cooling typically provides an acceptable balance, while thicker deposits exceeding 8 mm may require furnace cooling to prevent cracking.

The research also implicitly addresses the concept of post-weld heat treatment as an alternative to controlling the cooling method. While the study focuses on cooling rate effects, the underlying metallurgical principles are identical to those governing post-weld tempering operations. The residual stresses introduced during welding can be relieved through either slow cooling or subsequent tempering, and both approaches have their advantages depending on the production schedule and equipment availability.

Summary

This study provides engineers with a systematic framework for selecting cooling methods for wear-resistant overlay plates based on the desired balance between hardness and toughness. The key takeaway is that cooling rate is a powerful lever for tailoring mechanical properties, but it must be applied with consideration of cracking susceptibility and residual stress levels. For practical implementation, engineers should evaluate the specific alloy composition, deposit thickness, and component geometry before selecting a cooling method, recognizing that the optimal choice represents a compromise between wear resistance, fracture resistance, and manufacturing reliability.