Synopsis presentation

1. DEPARTMENT OF MATERIALS AND
METALLURGICAL ENGINEERING
SYNOPSIS REPORT ON
TRIBOLOGICAL BEHAVIOUR OF
NITRONIC -STEEL

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Introduction
Tribology is defined as the science and technology of interactive
surfaces in relative motion and it encompasses a study of friction wear
and lubrication.In modern industry, more and more new processes
have been used with higher efficiency, better liability. But for friction
and wear parts, that means higher speed and load, and less
maintenance.
Erosion of underwater parts is a serious problem encountered in hydro
power plants. Similar problems are also encountered in hydraulic
components, mining industries, dredging work, and waste disposals.
Underwater components of hydro turbines operating in silt (abrasive
particles) laden water suffer from extensive erosion. Due to high
amounts of silt damage it becomes impossible to run the unit for a
longer time thus incurring heavy loss of power generation.

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Currently 13Cr-4Ni martensitic stainless steel is used in underwater
parts in hydroelectric projects. It has limited wear life and frequent
repair/maintenance is needed.
Hydro Turbine blades in hydroelectric power plants are subjected to
erosion. The cast martensitic stainless steel containing 13%Cr and
4%Ni (wt %) currently find wide applications in hydro turbines and
other industrial equipment subject to erosion. This steel suffers from
several maintenance and welding related problems. The poor
weldability of this steel is due to formation of martensite during
welding.

4. Concept to be used
Erosion resistance increases with the increasing hardness at constant
ductility. When water bubbles collapse on a surface, the liquid adjacent to
the bubbles is at first accelerated and then suddenly decelerated as it
collides with the surface. The collision between liquid and solid generates
large stresses which can damage the solid. Transient pressures as high as
1.5 GPa are possible. This can cause cavitation erosion. The solid particle
erosion involves impact of eroding particles on a surface. The process
depends on the particle kinetic energy, impact angle, the particle shape,
properties of target-material, and environmental conditions. At lower
impact angles the mode of erosion is cutting and ploughing deformation.

5. During ploughing lip formation occurs due to deformation in the localized
regions near the surface of the target and lip is taken out either by inertial-
stress-induced tensile fracture or by separation across adiabatic shear
bands formed at the base of the lip. At high impact angles strain
hardening and flaking/pitting of the surface takes place.

6. Problem to be solved
Erosion of underwater parts made of steel, in hydro power plants with focus
on hydro turbine blades.

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Objective of the Project
To study cavitation erosion , solid particle erosion and sliding erosion in
hydro turbine blades and other products made of nitronic-steel
To study structure property correlation
To study comparison of erosion behaviour of 23/8N nitronic steel with
13/4 martensitic stainless steel and 316L stainless steel.
Work plan
Literature Review, if the situation is suitable then experiment will be
conducted.
Methodology
1.Materials (nitronic-steel and alloying elements): manganese ,nickel, carbon,
silicon, chromium, molybdenum
2.Cold Work: It is done to increase the strength of steel.

8. 3. Heat Treatment: This treatment is used to promote strain age hardening.
The samples are oil quenched after the correct ageing time.
4.Metallography
4.1. Optical microscopy: Light microscopy is performed in the
conventional bright field mode.In preparation for the light microscopy the
specimens are ground and final mechanical polishing is accomplished.
4.2. Scanning electron microscopy: All specimens are thoroughly cleaned
in alcohol and images are acquired using the secondary electron detector.
4.3. Transmission electron microscopy: A double tilt specimen holder is
used to obtain the correct imaging conditions.Both bright and dark field
imaging techniques are used to study stacking faults, twinning, dislocations
and precipitation.

9. 5. Tensile Tests: The resulting load versus extension data obtained from
the tensile testing machine is converted to true stress versus true strain.
The graphs of the engineering stress versus engineering strain curves are
then drawn using this data. The work hardening rate is obtained by plotting
the slope of the true stress vs. true strain curve against true strain.
6. Hardness and Microhardness Measurements: Macro hardness tests are
performed with a Vickers indenter, on a polished surface. At least five
hardness indentations are made and an average taken.
Microhardness is measured using a microhardness tester. A Vickers
indenter is used. At least ten indentations are performed and from this an
average of the micro hardness is calculated.

10. 7. X-ray Diffraction(XRD): XRD is used to assess whether or not any phase
transformation has taken place during cold deformation or cavitation
erosion.
8. Cavitation: A cavitation environment is produced. During cavitation the
specimen is removed from the sample holder and weighed every hour. The
volume loss is then calculated. When the cumulative volume loss is
plotted against the cavitation time a distinctive cavitation erosion curve
emerges.

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Timeline
Upto Mid Term: To study cavitation erosion , solid particle
erosion and sliding erosion in hydro turbine blades and other
products made of nitronic-steel
Upto End Term: To study structure property correlation ; To
study comparison of erosion behaviour of 23/8N nitronic steel
with 13/4 martensitic stainless steel and 316L stainless steel.