Corrosive wear of the Co-Cr-W alloy in liquid zinc
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Liang The Institute of Metals Research, Chinese Academy of Sciences, Shenyang 110015, People’s Republic of China (Received 11 April 2000; accepted 12 March 2001)
The corrosive wearing behavior of the Co–Cr–W alloy in liquid zinc was investigated using a specially designed wearing test machine. Its corrosion rate and wear rate during corrosive wearing process with different conditions were analyzed. The corrosive wearing mechanism of the Co–Cr–W alloy was investigated by analysis on its sliding surface using scanning electron microscopy, energy dispersive spectrometry, and microhardness sclerometer. The experimental results led to the following conclusions: (i) The corrosion of the Co–Cr–W alloy is accelerated by wearing process in the liquid zinc. (ii) The liquid zinc provides obvious lubrication to the sliding surfaces of this alloy and then reduces its wearing rate during the corrosive wearing process. (iii) Its corrosive wearing rate is increasing sharply with increasing temperature of the liquid zinc. (iv) The corrosive wearing of the Co–Cr–W alloy is caused by preferential corrosion of the eutectic phases in this alloy and fatigue cracking of the worn surface. The fatigue wearing of this alloy is directly due to the synthetic effect of strain hardening of the layer on and under sliding surface and serious stress corrosion in the crack tips during the corrosive wearing period.
I. INTRODUCTION
With the increasing demands for galvanized steel strips by the automobile and home electric apparatus industries the research of corrosion resistance materials against liquid zinc is attracting more attention in the materials research field.1– 4 For the comprehensive performance of mechanics at elevated temperature and corrosion resistance in liquid zinc, the Co–Cr–W alloy is often used to build some important parts, such as bearings for sink rolls in the current hot-dip galvanizing line.5 The corrosion of Co–Cr–W both in the presence of static and moving liquid zinc at 465 °C (the normal temperature of liquid zinc used in industrial hot-dip galvanizing line) was investigated.5 The research results indicated that the dynamic corrosion rate of this alloy was about 1.5 times higher than the static corrosion rate in liquid zinc. Its static corrosion was mainly caused by preferential corrosion of eutectic phases and uniform corrosion of Co-based ␥-phases by dissolution and alloying. The dynamic corrosion of this alloy was characterized as the preferential corrosion of grain boundaries and frequent breakage of the corroded surface layer, in addition dissolution and alloying. Therefore, it was considered that both eutectic phases and grain boundaries are the regions of this alloy most easily corroded in liquid zinc. J. Mater. Res., Vol. 16, No. 6, Jun 2001
Accordingly, to improve the corrosion resistance of the Co–Cr–W alloy used in liquid zinc, it is suggested that the amount of eutectic phases and the grain size of content of ␥-phases in the structure of this alloy should be limited. However, for the modern steel strip hot-
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