Wear Behavior of Austempered and Quenched and Tempered Gray Cast Irons under Similar Hardness

Bingxu Wang,Xue Han,Gary C Barber,Yuming Pan

doi:10.3390/met9121329

Abstract

In this research, an austempering heat treatment was applied on gray cast iron using various austempering temperatures ranging from 232 °C to 371 °C and holding times ranging from 1 min to 120 min. The microstructure and hardness were examined using optical microscopy and a Rockwell hardness tester. Rotational ball-on-disk sliding wear tests were carried out to investigate the wear behavior of austempered gray cast iron samples and to compare with conventional quenched and tempered gray cast iron samples under equivalent hardness. For the austempered samples, it was found that acicular ferrite and carbon saturated austenite were formed in the matrix. The ferritic platelets became coarse when increasing the austempering temperature or extending the holding time. Hardness decreased due to a decreasing amount of martensite in the matrix. In wear tests, austempered gray cast iron samples showed slightly higher wear resistance than quenched and tempered samples under similar hardness while using the austempering temperatures of 232 °C, 260 °C, 288 °C, and 316 °C and distinctly better wear resistance while using the austempering temperatures of 343 °C and 371 °C. After analyzing the worn surface, abrasive wear and fatigue wear with the presence of pits, spalls, voids, long cracks, and wear debris were the main mechanisms for austempered gray cast iron with a low austempering temperature. However, only small pits and short cracks were observed on the wear track of austempered gray cast iron with high austempering temperature. Furthermore, the graphite flakes were exposed and ground by the counterpart surface during wear tests. Then, the graphite particles would form a tribo-layer to protect the contact surface.

Highlights

Gray cast iron (GI) is one of the conventional iron-carbon alloys with a carbon content of 2.5–4%and a silicon content of 1–3%
As compared with the microstructure of as-cast GI in Figure 1, no changes could be found related to the characteristics of graphite flakes after receiving the austempering heat treatment
The original pearlitic structure was transformed into acicular ferrite and carbon saturated austenite, as shown in

Summary

Introduction

Gray cast iron (GI) is one of the conventional iron-carbon alloys with a carbon content of 2.5–4%. Its typical microstructure contains graphite flakes surrounded by pearlite or ferrite. Size, and distribution, graphite flakes are divided into five patterns from A to E in the ASTM Standard A247 [1]. Due to its excellent machinability and damping capacity with low production cost, GI has been broadly used in the manufacturing of brake rotors, clutch discs, cylinder liners, and tool mounts. Most of the GI applications require superior resistance to retard wear loss on contact surfaces.

Methods

Results

Conclusion