Repetitive impact wear of steels

Abstract A study has been conducted to determine the material, microstructural, design and operating parameters of importance in minimizing the impact wear of valves operating in hydropowered stoping mining equipment. Laboratory apparatus has been built capable of simulating the repetitive impact wear experienced by poppet valves. Testing has been conducted, using line contact specimens, on a variety of heat-treated alloy and stainless steels at frequencies between 5 and 50 Hz and impact energies from 2 to 5 J. The wear rates were found to be related to the impact energy in extended tests carried out on one steel (AISI 431) and followed an empirical power law of the type W = KNEn, where E is the impact energy, N the number of impacts, and K and n are constants. Under lubricated conditions, two wear mechanisms, i.e. pitting and surface traction, were observed. Considerably higher wear loss is associated with surface traction. Materials with high indentation hardnesses and associated low adhesion coefficients exhibited wear loss by pitting alone. Dry impacting produced much higher wear owing to surface heating. A high hardness, low coefficient of adhesion, adequate toughness and good corrosion resistance are all requirements for materials operating in such conditions. However, the most powerful means of reducing wear is to keep impact velocities as low as possible.