Galling of stainless steels as a function of test conditions in an ASTM G196-type test setup – The role of temperature, rotational velocity, interrupted rotation and rotational distance

Austenitic stainless steels have attractive properties for use in corrosive environments, but their use in components where motion under load is experienced (such as valves) is limited by their poor galling behaviour. Whilst stainless steels with improved performance have been developed over many years, the basic understanding of the key parameters in galling of standard stainless steels is not well understood. In this work, the galling behaviour of a dissimilar austenitic stainless steel pair is explored via testing in an instrumented ASTM G196-type test. Key variables examined are environmental temperature (room temperature and 100 °C), rotational speed (2.1 rpm and 5.5 rpm), and the sliding distance (from a quarter of a turn up to five turns). Galling was observed to become more severe with increased temperature, but was not significantly affected by either sliding speed (in the range examined) or interruptions during the rotation. The measurement of friction coefficient along with surface observations revealed that galling does not take place within the initial period of sliding; however, damage is being accrued by the sample surfaces which then results in subsequent observable galling as the sliding distance is increased. The importance of measuring torque during galling tests is illustrated, and the findings provide useful information with regard to those test variables that require critical control (and which do not) during conduct of a galling test programme.