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1. Presentation on
Low Alloy Steels
In nuclear

2. For more help contact me
Muhammad Umair Bukhari
Engr.umair.bukhari@gmail.com
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3. INTRODUCTION
• High strength low alloy (HSLA) steels are designed to provide
conventional carbon steels better mechanical properties
and/or greater resistance to atmospheric corrosion than a
hardening mechanism.
• The material for a pressure retaining component should have
a sufficient strength and fracture toughness for the assurance
of the structural integrity. For a nuclear reactor vessel, a
resistance to an irradiation embrittlement is also an
important property. In general, the fracture toughness of a
material is decreased when its strength is increased by a
hardening mechanism.

4. INTRODUCTION
Low-alloy steels (LAS) are widely used for pressure vessel and
piping in light water reactors. The reactor pressure vessel (RPV) is
the most critical pressure-boundary component as far as safety
and plant life are concerned. The possible effect of
environmentally- assisted cracking (EAC) on RPV structural
integrity, therefore, continues to be a key concern within the
context of both reactor safety and evaluation/extension of plant
service life.

5. INTRODUCTION
The HSLA steels have low carbon contents (0.05-0.25% C) in order
to produce adequate formability and weldability, and they have
manganese contents up to 2.0%. Small quantities of chromium,
nickel, molybdenum, copper, nitrogen, vanadium, niobium,
titanium and zirconium are used in various combinations.

6. The various types of Microalloyed
• Vanadium microalloyed steels
• Niobium microalloyed steels
• Niobium-molybdenum steels
• Vanadium-niobium microalloyed steels
• Vanadium-nitrogen microalloyed steels
• Titanium microalloyed steels
• Niobium titanium microalloyed steels
• Vanadium-titanium microalloyed steels

7. HEAT TREATMENTS OF LOW ALLOY
STEELS
• Most of the engineering properties of metals and alloys are
related to their structure. Equilibrium structure can be
predicted for an alloy with the help of an equilibrium
diagram.
• Mechanical properties can be changed by varying the relative
proportions of micro constituents. In practice, change in
mechanical properties is achieved by a process known as heat
treatment.
• This process consists of heating a metal or alloy to a specific
predetermined temperature, holding at this temperature for
required time, and finally cooling from this temperature. All
these operations are carried out in solid state.

8. Heat treatment may be undertaken for the
following purposes:
• Improvement in ductility
• Relieving internal stresses
• Refinement of grain size
• Increasing hardness or tensile strength

9. RADIATION EMBRITTLEMENT OF LOW-ALLOY
STEELS
• Neutron irradiation of reactor pressure vessel (RPV) steels
increases density of point defects, enhances diffusivity of all
atoms in solid solution and produces phase transformations,
precipitation, micro voids, etc. that results in considerable
change in mechanical properties of low-alloy steels.
• The most dangerous of them are the loss of plasticity and
increase of brittle fracture. The prediction of radiation
embrittlement of RPV materials during their operation is of
great applied importance.

10. CHARACTERIZATION of Ni–Mo–Cr LOW ALLOY
STEELS FOR NUCLEAR APPLICATION
• The Mn–Mo–Ni low alloy steels such as SA508 Grade 3 and
SA533 Grade B, have been used widely for nuclear reactor
pressure vessels for more than 30 years due to a combination
of their good strength, toughness and weldability in addition
to economy.
• Several types of advanced PWR’s (pressurized water reactors)
are under development, which are from a smaller
modularized reactor to a much larger capacity reactor than
the currently operating reactors.
• ferritic low alloy steels still have a priority under the
operating conditions of PWR type reactors.
• , Ni and Cr are known to be effective elements for an increase
of the hardenability of ferritic steels.

11. EFFECT OF CYCLIC STRAIN RATE ON LOW
ALLOY STEEL
• Low alloy steels (LASs) used as the structural materials of
nuclear power plants (NPPs) are subject to cyclic stress during
plant operation. Consequently, fatigue damage is one of the
most significant degradation mechanisms of them.
• Moreover, fatigue crack growth rate is accelerated in the high
temperature water environment of NPPs, thereby reducing
the fatigue life Therefore, the environmental fatigue
behaviors of LASs should be considered to assess the integrity
and the safety of NPPs.