Study of surface roughness and hardness of low carbon nickel-chromium based alloy steels under high temperature (AISI sae8630, 3140 & 9310)
High temperature Tribology is an interesting and challenging area which deserves more attention on wear resistance. The present investigation relates to understanding the surface roughness and hardness by the effect of different operational conditions like wear pressure, sliding speed and ambient temperature on AISI SAE 8630, 3140, and 9310. Dry sliding wear tests have been carried out on the materials AISI SAE 8630, 3140, and 9310 under room temperature and also at high temperatures like 200°C, 400°C and 600°C on pin on disc type wear testing machine for 10,000 m sliding distance. The wear tests were carried out under the operational conditions of three sliding speeds like 1, 3 and 5 m/s, under the wear pressures of 0.125 MPa, 0.375 MPa and 0.625 MPa. Weight loss was recorded after each wear test. Hardness after wear was measured by micro hardness tester under 100 gm wear pressure. Roughness of the worn-out surface along the parallel & perpendicular was measured by roughness instrument.
 The present investigation was undertaken keeping in view the wear behaviour of metallic material influenced by the frictional force, which is turn, is governed by the hardness & oxidation kinetics of the mating surface on the high temperature wear. Nickel Chromium based alloys have been reported to be widely used as they combine several advantages such as abrasion, erosion & resistance to high temperature corrosive atmospheres. In this article a brief review of the performance of Nickel Chromium based alloy at different speeds, loads and temperatures has been made and compared with the room temperature.
 It is observed that the hardness of the worn out surface increased with an increase in the load and sliding speed due to work hardening at room temperature. Under low operational conditions, two body abrasive, under high operational conditions oxidative and under moderate operational conditions adhesive wear mechanisms are observed.
Cavitation erosion of iron and steel
A study has been made of the mechanisms and rates of cavitation erosion of iron and plain carbon steels. The high strain rate produced by cavitation results in the development of high densities of deformation twins in iron and the subsequent erosion of the metal by cleavage fracture. Erosion of the ferrite phase also dominates the failure of the normalized and spheroidized steels and, consequently, their erosion resistance is negligibly greater than that of the iron. Only the martensitic structure exhibits a significantly improved resistance. These results imply that a coarse (1 to 2 µm) second phase is not sufficient to provide protection against cavitation and that a change in the strength of the weakest phase—in this case, the ferrite—is required for an increased incubation period and decreased erosion rate.
Intelligent cavitation diagnostics and monitoring
A detailed insight into cavitation processes in turbines is possible through a new multi-dimensional technique. The method is useful in all phases of the turbine's life and provides a sound base for a rational but reliable maintenance scheme. Branko Bajic reports.