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Heat Treatment Processes
Task 1 – “Scenario
When manufacturing products, decisions must be made on material properties to meet the specification
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Assignment
1
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You are required to provide clear written instructions
to the workshop for the operation as follows:
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Describe in detail the process of surface hardening the teeth only of the gear wheel
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Use sketches and diagrams as necessary to help with your information
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As a manufacturing engineer, you have a quantity of 12mm square section mild steel which has to be cold formed into shape for a
project
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To prevent
this problem occurring on future parts, you conclude that the steel bar must be fully annealed before bending
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In a written reference guide, describe in detail the annealing process you would use
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Use diagrams as appropriate
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For the two scenarios above, you must also report to the health and safety committee
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1- The process of making the teeth of a gear wheel hard, but leaving the core ductile, is called
Flame Hardening, it is a type of Surface Hardening process
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Once the material is heated
at the depth that they want it to be hardened, a water/high pressured air jet would follow on
behind to cool the material instantly to make it hard
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The gear wheel
is Medium Carbon Steel, so the carbon content is 0
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9% Carbon, at this carbon content,
the first tooth needs to be heated up to 725°C to 785°C, in the upper critical Temperature
zone
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The water jet quenches the tooth which is rapid cooling, which
produces a very hard structure known as martensite (Very hard form of steel crystalline
structure)
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Once the tooth is complete,
the next tooth can be started using the same process, keep going until all the teeth are done
on the gear wheel
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Water (Cooling Source)
Follow straight after the
flame to cool the teeth
down straight after
heating
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Flame (Heat
Source) To
heat the
material to
specific
temperature
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If the material gets annealed, the molecules get agitated and frees up more, at which
point, in the end of the process, the material would bend easily as the molecules within the
material would have changed and make the material more ductile
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At this
stage, is reliable to fracture or crack if people bend it whilst the material is cold
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05% to 0
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To anneal the steel, it should be heated to between 850°C
and 950°C, above upper critical temperature
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After the steel
have cooled down, it should be softer and it should be ductile, if the steel is to be bent after
it has been annealed, the steel shouldn’t have and stress marks and it should give a smooth
bend with a better quality finish
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One legislation that goes with the processes is ‘The Acetylene Safety Regulation 2014’, This is
one legislation that would apply as sometime the gas used to heat material contains
acetylene, oxy-acetylene is usually the best way to transfer heat as it would work in any
temperature, whether it is cold in the winter or warm in the summer which oxy-propane isn’t
just as good as oxy-acetylene
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Another legislation that would apply is the ‘Health and Safety at Work act 1974’, this applies
as the employers have general duties to their employees and to make sure they are safe with
free PPE that should be provided to the employees and make sure they have proper training
on the equipment and to make sure they use it sensibly
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Assignment
Prepare a written report to justify your choice of solution for the following scenarios:
1
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State and briefly describe the process you would use then explain why it is appropriate
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You are using mild steel with a carbon content of 0
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Identify the problem you need to address and describe the solution in detail, including all steps
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Heat Treatment Processes
You need to add an additional slot to a high carbon steel bush which had previously been hardened and tempered
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Identify a heat treatment process that may be applied to the steel
component to overcome the problem
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State how you would ensure
the component is returned to its original condition before being placed back in service
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The heat treatment I would use would be ‘Hardening’
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After the steel is heated up, it is to then be quenched in cold oil, I believe that
oil is a better idea then if it was quenched in water
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The rate of cooling of oil isn’t as good as rate of
cooling with water, but it is still quick
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After the steel is hardened
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2

The mild steel shaft has a 0
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The core of the shaft needs to stay ductile so
the core does not fracture or crack whilst being used, but the outer surface need to be
hardened so it can withstand damage
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Induction
heating is used when the outer surface of a material needs to be heated up, but the core
would stay at normal temperature to keep it ductile
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By producing the currents in the surface layers,
the current heats the surface quick enough so that it will not heat the core to a high enough
temperature for hardening before the material gets quenched
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2% carbon content, so the outer surface needs to be heated up to
885°C, at the Upper Critical Temperature zone
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When the whole material has been heated, it is then quenched (rapid cooling process) with
either water or oil, the faster the cooling is, the harder the material will be
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Current of steel

Current of coil

Current of

3
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Also it has been tempered as
well which should make it a bit ductile
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Normalising is where a piece of metal gets the Normalising heat
treatment to change it back to its original state which makes it appropriate to change the
steel back to normal so it is easier to cut as it would be softer and not hardened anymore
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To change the high carbon steel bush back to normal, the first thing to do, is to heat the
whole material evenly to 40°C above the Upper Critical Temperature
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After a short period of time has passed, the
steel should then be left to cool itself down in air
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Once the material has cooled down back to normal temperature, the material
should be more than enough back to its original state and should be easier to cut with the
high speed steel cutter without the blades blunting
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Personally I would use oil due to it quenches, not as quick as
water but still quite rapid however it would fracture or crack the high carbon steel, which
water has a risk of fracturing or cracking the material
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After the material is hardened, I would then
temper the material, this makes it more ductile at the expense of hardness and brittleness
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This
process would make the high carbon steel bush ductile, as well as hard again ready to go
back into service
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Another way to test whether or not the centre punch has been hardened, is to
try and scratch the centre punch
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(Question Task 2 – 2 redo)

Heat Treatment Processes

The mild steel shaft has a 0
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The core of the shaft needs to stay ductile so
the core does not fracture or crack whilst being used, but the outer surface need to be
hardened so it can withstand damage
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Case hardening is appropriate as Case hardening can be used when there are steel with a low
carbon content that needs hardening
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03mm
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First, I would heat the steel to a temperature of around about 930°C to 970°C (steel with be
on a red heat)
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After the steel have been allowed to cool down a little, I would then heat the steel again to a
red heat (800°C to 950°C, depending on the carbon content)
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The steel should now acquire a
hardened outer surface, but a soft, ductile core
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