Cavitation erosion and hydroabrasion resistance of cold work tool steels produced by powder metallurgy

Abstract

Carbide-rich cold work tool steels produced by powder metallurgy are designed for applications that are exposed to heavy abrasive wear. Alloying with higher amounts of chromium and molybdenum additionally leads to corrosion resistance. This makes them excellent candidates for use in fluid flow systems with a high abrasive load, e.g. due to liquids containing sand particles. In this study, two different cold work tool steels were examined with focus on wear attack that may occur in combination with flowing liquids. On one hand, hydroabrasive attack results from fluids containing abrasives such as sand. This was simulated using a slurry pot containing a mixture of water and SiO2 particles. On the other hand, changes in flow speed may cause formation of cavitation bubbles that lead to erosive wear of the surfaces of nearby materials. Thus, despite the fact that resistance to surface spalling (e.g. by cavitation) was not a primary goal of alloy development, both alloys were also investigated by means of ultrasonic cavitation testing. The aim was to detect the influences of alloying system, processing route, and heat treatment condition on the wear resistance. The results indicate a positive influence of retained austenite on cavitation resistance, whereas the exact opposite holds true in the case of hydroabrasion. The damage mechanisms were analyzed by means of optical as well as scanning electron microscopy with special focus on the role of carbides during cavitation. Further attention was paid to the manufacturing route by comparing commonly used hot isostatic pressing (HIP) with supersolidus liquid phase sintering (SLPS). The latter permits consolidation of pre-alloyed powders to near net-shape parts or to thick protective layers on lower alloyed substrates. Compared to HIP, SLPS promises lower manufacturing costs combined with comparable mechanical properties.