INTRODUCTION
As we know there is a little bit of steel in everybody life. Steel has many practical
applications in every aspects of life. Steel with favourable properties are the best
among the goods. The steel is being divided as low carbon steel, high carbon steel,
medium carbon steel, high carbon steel on the basis of carbon content.
Low carbon steel has carbon content of 0.15% to 0.45%. Low carbon steel is the
most common form of steel as it’s provides material properties that are acceptable
for many applications. It is neither externally brittle nor ductile due to its lower
carbon content. It has lower tensile strength and malleable. Steel with low carbon
steel has properties similar to iron. As the carbon content increases, the metal
becomes harder and stronger but less ductile and more difficult to weld [2].
Steel is an alloy of iron with definite percentage of carbon ranges from 0.15-1.5%,
plain carbon steels are those containing 0.1-0.25%. There are two main reasons for
the popular use of steel: (1) It is abundant in the earth’s crust in form of Fe2O3 and
little energy is required to convert it to Fe. (2) It can be made to exhibit great variety
of microstructures and thus a wide range of mechanical properties. Although the
number of steel specifications runs into thousands, plain carbon steel accounts for
more than 90% of the total steel output. The reason for its importance is that it is a
tough, ductile and cheap material with reasonable casting, working and machining
properties, which is also amenable to simple heat treatments to produce a wide
range of properties. They are found in applications such as train railroads, beams for
building support structures, reinforcing rods in concrete, ship construction, tubes for
boilers in power generating plants, oil and gas pipelines, car radiators, cutting tools
etc [2] [3].
Principles of heat treatment for steels have been well-studied and are well-
understood. These principles provide the basis for heat treatment specifications and
practices used by heat treaters and steel foundries on a daily basis. While current
heat treatment specifications provide general guidelines for the heat treatment of
steel castings, they do not address all critical aspects of steel casting heat treatment
practice. A wide range of heat treatment equipment and heat treatment control
strategies are used in today’s steel foundries. Modern temperature data acquisition
systems allow increased knowledge of the thermal conditions in a furnace load, not
just in the furnace itself. This improvement in technology affords the possibility of
load-based heat treatment time and temperature cycles, which are more precise
than heat treatment cycles based on furnace temperature. Challenges in
temperature monitoring of loaded furnaces
have led to overly conservative practices to ensure complete heating of casting
loads. Commonly used “hour-per-inch” rules are used to ensure that the centres of
casting loads in heat treatment furnaces reach the appropriate temperature.
However, these practices often result in holding castings at temperature far longer
than is necessary.
For example, current heat treatment specifications for high alloy steels prescribe
only the minimum heat-treating temperatures and the quenching media. Variations
in furnace conditions, furnace loading,
quench delay, quench tank temperature, and quenchant velocity are not addressed
in the current specifications. However, it is clear that these parameters must be
carefully controlled to develop a successful heat treatment practice [3].
The process heat treatment is carried out first by heating the metal and then cooling
it in water and air. The purpose of heat treatment is to soften the metal, to change
the grain size, to modify the structure of the material and relive the stress set up in
the material. The various heat treatment process are annealing, normalizing,
hardening, austempering, tempering and surface hardening.
1.1 Overview of work done
In this Project Heat treatment of specimens of H11 and H13 (Hot work tool steels or
Chromium based steel) was done in open hearth furnace. Two specimens of each of
H11 and H13 went through heat treatment, one specimen of each material was
water quenched and other were air quenched. The mechanical properties such as
impact strength and hardness before and after the Heat treatment were studied.
Also surface topology, relative abundance of chemicals and crystal structures were
also studied using SEM, EDS and XRD tests respectively.
