High-Temperature Wear Resistance of Valve Sealing Surface Overlay Materials

Literature Overview

This classic study by Yao Shoushan, Lu Hao, Zhu Yanping, Hu Wenzheng, Gu Pujin, and Pan Dayou from the Department of Materials Engineering at Shanghai Jiaotong University and Shanghai Power Plant Auxiliary Machinery Factory investigates the adhesive wear behavior of valve sealing surface overlay materials from room temperature to 600°C. Published in the Journal of Shanghai Jiaotong University, 1996, Vol. 30, Issue 8, pages 120-124, this work addresses the critical challenge of valve seat sealing in high-temperature power plant applications, where valve components are subjected to severe adhesive wear during repeated opening and closing cycles.

Core Technical Findings

Test Materials and Conditions

Four overlay materials were evaluated:

Material Designation	Type	Base Alloy System	Application
D802	Electrode	Cobalt-based (Stellite)	High-temperature wear
NDG-2	Powder	Nickel-based	Corrosion and wear
D547Mo	Electrode	Iron-based (high Mo)	General wear
D507Mo	Electrode	Iron-based (Mo)	General wear

Adhesive wear tests were conducted from room temperature to 600°C, with systematic variation of counter-material and pairing configuration.

Key Results

The study establishes three fundamental findings:

Counter-material effect: The pairing material significantly influences the wear resistance of the overlay. Harder counter-materials generally produce less adhesive wear on the overlay surface.
Pairing configuration effect: The arrangement of materials in the sliding contact affects wear behavior, with different configurations producing different wear mechanisms.
Temperature effect: Wear resistance generally degrades with increasing temperature due to softening of the matrix, enhanced diffusion, and altered surface chemistry.

Wear Mechanism Analysis

Through high-temperature hardness testing, high-temperature metallography, and electron metallography, the study elucidates the high-temperature adhesive wear mechanism:

At lower temperatures: Mechanical deformation and plastic flow dominate the wear process.
At intermediate temperatures: Thermal softening reduces yield strength, promoting material transfer at contact asperities.
At high temperatures (near 600°C): Diffusion-controlled material transfer becomes significant, and oxide formation at the contact interface plays a complex role in either protecting or accelerating wear.

Comparative Performance

Material	Room Temperature Wear	High Temperature Wear	Mechanism Dominant
D802 (Co-based)	Excellent	Good	Mechanical resistance
NDG-2 (Ni-based)	Good	Moderate	Oxide film formation
D547Mo (Fe-based)	Moderate	Poor	Thermal softening
D507Mo (Fe-based)	Moderate	Poor	Thermal softening

Engineering Practice Implications

Material Selection for Valve Sealing Surfaces

Based on the study findings, the following selection guidelines are recommended for power plant valve applications:

For temperatures above 500°C: Cobalt-based Stellite alloys (D802) are preferred due to their superior high-temperature strength retention and resistance to adhesive wear.
For temperatures 300-500°C: Nickel-based alloys (NDG-2) offer a good balance of wear resistance, corrosion resistance, and cost.
For temperatures below 300°C: Iron-based Mo alloys (D547Mo, D507Mo) may be acceptable for cost-sensitive applications.
Counter-material matching: The valve stem and seat should be designed as a matched pair, considering the interaction between both surfaces during sliding contact.

Design Considerations for High-Temperature Valve Seals

Thermal expansion mismatch: Differential expansion between the overlay and base material can cause seal degradation at elevated temperatures.
Stress relief requirements: Post-weld stress relief is essential to prevent cracking in the overlay during thermal cycling.
Surface preparation: The base material surface condition significantly affects overlay adhesion and subsequent wear performance.
Overlay thickness: Sufficient thickness is required to accommodate material loss during service while maintaining the sealing geometry.

Study Insights and Reflections

This 1996 study remains remarkably relevant to contemporary valve engineering practice, particularly for power plant applications where high-temperature valve sealing continues to be a major reliability concern. The systematic approach of varying temperature, counter-material, and pairing configuration provides a comprehensive understanding of the wear mechanism that goes beyond simple material ranking. The finding that iron-based overlays degrade significantly at high temperatures while cobalt-based alloys maintain performance validates the continued use of Stellite-type alloys for critical high-temperature valve applications despite their higher cost. For modern engineers, this work serves as a valuable reference for understanding the fundamental wear mechanisms that govern valve seal performance, and the insights gained from this research can be applied to the selection of overlay materials for next-generation power plant valves operating under even more demanding conditions. The methodology employed, combining laboratory testing with microstructural analysis, exemplifies the rigorous approach needed to develop reliable engineering solutions for critical components.