Phase Diagrams - Revision history

DT Online at 10:00, 2 April 2017

2017-04-02T10:00:10Z

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	If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' such that, when a certain percentage of '''Carbon''' is exceeded, the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present, then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.		If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' such that, when a certain percentage of '''Carbon''' is exceeded, the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present, then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.

			----
			<span style="color: green">'''Note:'''
			Particular names are given to other compositions of '''Iron''' and '''Carbon''' which occur under certain time and temperature conditions e.g.:</span>
			* <span style="color: green">[https://en.wikipedia.org/wiki/Ledeburite '''Ledeburite'''] is a Eutectic alloy of Iron and Carbon containing about 4.3% Carbon.</span>
			* <span style="color: green">[https://en.wikipedia.org/wiki/Bainite '''Bainite'''] is a plate-like microstructure that forms in steels at temperatures of 250–550 °C</span>

			----

DT Online: Malleable and Ductile Cast iron

2017-04-02T09:07:03Z

Malleable and Ductile Cast iron

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	[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is ~~so called because on~~ cooling from its molten state, the additional '''Carbon''' is given time to separate out ~~and~~ form flakes of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] within the '''[[Crystalline Structures\|Crystalline Structure]]'''. The [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] flakes not only give rise to a grey appearance, hence the name, but are also self-lubricating which enables [https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] to be machined ‘dry’ ''(i.e. without additional coolant)''.		[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is the most commonly used [https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron''']. It is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' to which up to 3% [https://en.wikipedia.org/wiki/Silicon '''Silicon'''] is added. On cooling from its molten state, the additional '''Carbon''' is given time to combine with the [https://en.wikipedia.org/wiki/Silicon '''Silicon'''] and separate out to form flakes of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] within the '''[[Crystalline Structures\|Crystalline Structure]]'''. The [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] flakes not only give rise to a grey appearance, hence the name, but are also self-lubricating which enables [https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] to be machined ‘dry’ ''(i.e. without additional coolant)''.


	By contrast, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] is cooled quickly which suppresses the formation of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] and causes the extra '''Carbon''' to precipitate out as '''Cementite'''		By contrast, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] is cooled quickly, which suppresses the formation of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] and causes the extra '''Carbon''' to precipitate out as '''Cementite'''. As a consequence, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] is extremely '''[[Hardness\|Hard]]''' and too '''[[Brittleness\|Brittle]]''' for most applications.


			[https://en.wikipedia.org/wiki/Cast_iron#Malleable_cast_iron '''Malleable Cast Iron'''] and [https://en.wikipedia.org/wiki/Ductile_iron '''Ductile Cast iron'''] have a similar composition to [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] with the exception that it is cooled more slowly via a controlled process which causes the surplus '''Carbon''' to form spheroidal particles of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] rather than flakes ''(i.e. [https://en.wikipedia.org/wiki/Ductile_iron '''Spheroidal Graphite'''])''. The rounded shape of the sphere-shaped [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] inclusions at the grain boundaries reduce any '''[[Stress Concentration]]''' and limit the propagation of cracks.




	[[Category:Materials and Components]]		[[Category:Materials and Components]]

DT Online at 08:26, 2 April 2017

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	<span style="color: green">'''Note:'''		<span style="color: green">'''Note:'''
	For simplicity the small ~~areas~~ of single phase [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] on the left of the diagram ~~and single phase '''Carbon''' on the right have~~ been omitted.		For simplicity the small area of single phase [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] on the left of the diagram has been omitted.
	</span>		</span>
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DT Online at 22:12, 1 April 2017

2017-04-01T22:12:36Z

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	=====Cast ~~iron~~=====		=====Cast Iron=====

	[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.		[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.

DT Online at 22:09, 1 April 2017

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	[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is so called because on cooling from its molten state, the additional '''Carbon''' is given time to separate out and form flakes of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] within the '''[[Crystalline Structures\|Crystalline Structure]]'''. The [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] flakes not only give rise to a grey appearance, hence the name, but are also self-lubricating which enables [https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] to be machined ‘dry’ ''(i.e. without additional coolant)''.		[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is so called because on cooling from its molten state, the additional '''Carbon''' is given time to separate out and form flakes of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] within the '''[[Crystalline Structures\|Crystalline Structure]]'''. The [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] flakes not only give rise to a grey appearance, hence the name, but are also self-lubricating which enables [https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] to be machined ‘dry’ ''(i.e. without additional coolant)''.

	By contrast, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] is cooled quickly which suppresses the formation of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] and causes the extra ''Carbon''' to precipitate out as '''Cementite'''
			By contrast, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron '''White Cast iron'''] is cooled quickly which suppresses the formation of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] and causes the extra '''Carbon''' to precipitate out as '''Cementite'''

DT Online at 22:08, 1 April 2017

2017-04-01T22:08:27Z

Show changes

DT Online: Added Cast iron

2017-04-01T20:00:22Z

Added Cast iron

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	[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.		[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.


			[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is so called because on cooling from its molten state, the additional '''Carbon'' is given time to separate out and form [[https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagrams'''] are charts which show how different '''Phases''' can exist together under certain conditions ''(e.g. the temperature range at which water and ice can exist together in slushy conditions)''. Three obvious '''Phases''' are the three states of matter: [https://en.wikipedia.org/wiki/Solid '''Solid'''], [https://en.wikipedia.org/wiki/Liquid '''Liquid'''], and [https://en.wikipedia.org/wiki/Gas '''Gas'''] but different '''Phases''' also exist when two or more liquids or solids come into contact with each other and form distinctive '''[[Crystalline Structures]]''' for example.


			{{#ev:youtube\|KQ5MjJndHp8\|300x250\|right\|\|frame\|loop=1&autoplay=0&playlist=KQ5MjJndHp8}}
			__TOC__


			In [https://en.wikipedia.org/wiki/Metallurgy '''Metallurgy'''] we are normally concerned with just [https://en.wikipedia.org/wiki/Solid '''Solid'''] and [https://en.wikipedia.org/wiki/Liquid '''Liquid'''] phases plus situations where these might exist together. The temperature line above which everything is [https://en.wikipedia.org/wiki/Liquid '''Liquid'''] is known as the [https://en.wikipedia.org/wiki/Liquidus '''Liquidus'''] and the line below which everything is [https://en.wikipedia.org/wiki/Solid '''Solid'''] is known as the [https://en.wikipedia.org/wiki/Solidus_(chemistry) '''Solidus'''].

			----
			<span style="color: green">'''Note:'''
			DT Online makes no attempt to explore the full depths of the fascinating topic of '''Metallurgy''' but hopes that the brief introduction given will stimulate interest and lead to further study. See the full series of lectures on [https://youtu.be/KQ5MjJndHp8?list=PL31C1F16DE82C106A '''YouTube'''] ''(‘A’ Level Chemistry and beyond)''.
			</span>
			----

			=====Cooling Curves=====
			[[File:LeadandTinCoolingCurves.png \|400px\|right\|Lead and Tin Cooling Curves]]

			Plotting a graph of '''Temperature''' and '''Time''' as liquid metal cools will produce a [https://en.wikipedia.org/wiki/Cooling_curve '''Cooling Curve''']. Such graphs serve to illustrate the behaviour of metal as it cools and what changes occur at different temperatures.


			Typical [https://en.wikipedia.org/wiki/Cooling_curve '''Cooling Curves'''] for pure metals will be a stepped graph as shown. Heat is being lost throughout the process but at the point of freezing the temperature doesn't fall because the freezing process will liberate heat at exactly the same rate that it is being lost to the surroundings.


			This is the result of energy being released when new atomic bonds are formed formed ''(e.g changing states from Liquid to Solid Lead or Tin)''.
			[[File:TinLeadAlloyCoolingCurve.png \|250px\|right\|Lead and Tin Cooling Curves]]


			The [https://en.wikipedia.org/wiki/Cooling_curve '''Cooling Curve'''] for an '''[[Alloy]]''' is more complicated and reveals interesting behaviours as solidification takes place.


			With this particular '''[[Alloy]]''', nothing happens at the normal freezing point of '''Lead''' because the addition of '''Tin''' has lowered this. Some solidification of '''Lead''' starts around 250<sup>0</sup>C but '''Tin''' remains liquid and there is not enough energy released to cause the [https://en.wikipedia.org/wiki/Cooling_curve '''Cooling Curve'''] to go horizontal - although it does flatten out because cooling slows down a little.


			The temperature stops falling at 183<sup>0</sup>C when both the '''Tin''' and '''Lead''' are starting to freeze. Once everything has solidified, the temperature continues to fall.


			=====Phase Diagram for Lead/Tin Eutectic Alloy=====
			[[File:SolderPhaseDiagram.png\|300px\|right\|Lead Tin Alloy Phase Diagram]]

			[https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagrams'''] combine the information from the [https://en.wikipedia.org/wiki/Cooling_curve '''Cooling Curves'''] of mixtures of metals with metals and with other elements to create a chart which is used to show the behaviours of different '''[[Alloy]]''' compositions as they change phases between [https://en.wikipedia.org/wiki/Solid '''Solid'''] to [https://en.wikipedia.org/wiki/Liquid '''Liquid'''] states.


			The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] for the '''[[Eutectic Alloy]]''' of 62% '''Tin''' & 38% '''Lead''' shows that at 183<sup>0</sup>C it changes from : [https://en.wikipedia.org/wiki/Liquid '''Liquid'''] to [https://en.wikipedia.org/wiki/Solid '''Solid'''] without going through any ‘pasty’ stage which makes it ideal for Tinman's Solder.
			[[File:SteelPhaseDiagram.png\|300px\|right\|Lead Tin Alloy Phase Diagram]]


			=====Phase Diagram for Carbon Steel=====

			As [https://en.wikipedia.org/wiki/Carbon_steel '''Carbon Steels'''] are heated towards their melting point their '''[[Crystalline Structures]]''' change from a '''[[Crystalline Structures\|Body Centred Cubic]]''' structure to a '''[[Crystalline Structures\|Face Centred Cubic]]''' structure. A consequence of this is that '''Iron''' heated above this '''Critical Point''' can absorb a lot more '''Carbon''' within a '''[[Crystalline Structures\|FCC]]''' structure.


			[https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] can be taken as just another name for '''Iron''' and, at room temperatures, it can absorb only a very small amount of '''Carbon''' ''(i.e. about 0.006%)'' within its single phase '''[[Crystalline Structures\|BCC]]''' structure.


			But immediately above 723°C '''Iron''' changes to a different single phase '''[[Crystalline Structures\|FCC]]''' structure called [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] and now can absorb up to about 0.8% carbon - and this increases with rising temperature. [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] can only exist at this elevated temperature and so as it cools all the extra '''Carbon''' has to go somewhere.

			----
			<span style="color: green">'''Note:'''
			For simplicity the small areas of single phase [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] on the left of the diagram and single phase '''Carbon''' on the right have been omitted.
			</span>
			----

			=====Ferrite, Cementite, Pearlite and Martensite=====

			The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] shows that for '''Steels''' with less than about 0.8% '''Carbon''' ''(i.e. Hypo Eutectic Steel)'' the mix solidifies into a two phase structure containing [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] which is very '''[[Hardness\|Soft]]''' and '''[[Ductility\|Ductile]]''', and a layered structure of both [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] and [https://en.wikipedia.org/wiki/Cementite '''Cementite''' ''(aka '''Iron Carbide''')''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' - really a [https://en.wikipedia.org/wiki/Ceramic '''Ceramic''']. This layered structure is called [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] because of its appearance.


			If cooled slowly, the '''Steel''' is stronger because of the added [https://en.wikipedia.org/wiki/Cementite '''Cementite'''] but still quite workable because large grains are given time to form and create space for '''[[Crystalline_Structures#Dislocations\|Dislocations]]''' to move. The more [https://en.wikipedia.org/wiki/Cementite '''Cementite'''] the harder the metal, the more [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''], the softer it will be.


			'''Steel''' with about 0.8% '''Carbon''' is known as '''Eutectoid Steel''' and at this concentration of '''Carbon''', the grain structure is completely [https://en.wikipedia.org/wiki/Pearlite '''Pearlite''']. In '''Steel''' with more than about 0.8% of '''Carbon''' ''(i.e. Hyper Eutectoid Steel)'' there is too much '''Carbon''' to just form [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] and a mixture of [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] with additional [https://en.wikipedia.org/wiki/Cementite '''Cementite'''] precipitating out at the grain boundaries is formed.


			If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' such that, when a certain percentage of '''Carbon''' is exceeded, the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present, then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.


			=====Tool Steel=====
			[[File:IronCarbonPhaseDiagram.png\|500px\|right\|Iron Carbon Phase Diagram]]

			When [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] with a very low '''Carbon''' content is '''Quenched''' the resulting '''[[Crystalline Structures\|BCC]]''' structure can accommodate the extra '''Carbon''' atoms and no great distortion takes place so the '''Steel''' is relatively unaffected by this rapid cooling. It is for this reason that '''Mild Steel''' cannot be '''[[Heat Treatment\|Hardened and Tempered]]''' but '''Tool Steel''' can.


			<span style="color: green">'''Note:'''
			The approximate, workshop ‘rule of thumb’, '''Carbon''' percentages for '''Mild Steel''' and '''Tool Steel''' are indicated but in reality, there are many much more precise [https://en.wikipedia.org/wiki/SAE_steel_grades '''SAE Grades'''] of [https://en.wikipedia.org/wiki/Carbon_steel '''Carbon Steel'''] available to suit the wide range of applications for this very versatile engineering material.
			</span>


			=====Cast iron=====

			[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.


			[https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] is so called because on cooling from its molten state, the additional '''Carbon''' is given time to separate out and form flakes of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] within the '''[[Crystalline Structures\|Crystalline Structure]]'''. The [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] flakes not only give rise to a grey appearance, hence the name, but are also self-lubricating which enables [https://en.wikipedia.org/wiki/Gray_iron '''Grey Cast Iron'''] to be machined ‘dry’ ''(i.e. without additional coolant)''.

			By contrast, [https://en.wikipedia.org/wiki/Cast_iron#White_cast_iron ''White Cast iron'''] is cooled quickly which suppresses the formation of [https://en.wikipedia.org/wiki/Graphite '''Graphite'''] and causes the extra ''Carbon''' to precipitate out as '''Cementite'''


	[[Category:Materials and Components]]		[[Category:Materials and Components]]

DT Online: Added Iron Carbon Phase Diagram

2017-04-01T19:34:37Z

Added Iron Carbon Phase Diagram

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			=====Ferrite, Cementite, Pearlite and Martensite=====

	The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] shows that for '''Steels''' with less than about 0.8% '''Carbon''' ''(i.e. Hypo Eutectic Steel)'' the mix solidifies into a two phase structure containing [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] which is very '''[[Hardness\|Soft]]''' and '''[[Ductility\|Ductile]]''', and a layered structure of both [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] and [https://en.wikipedia.org/wiki/Cementite '''Cementite''' ''(aka '''Iron Carbide''')''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' - really a [https://en.wikipedia.org/wiki/Ceramic '''Ceramic''']. This layered structure is called [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] because of its appearance.		The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] shows that for '''Steels''' with less than about 0.8% '''Carbon''' ''(i.e. Hypo Eutectic Steel)'' the mix solidifies into a two phase structure containing [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] which is very '''[[Hardness\|Soft]]''' and '''[[Ductility\|Ductile]]''', and a layered structure of both [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] and [https://en.wikipedia.org/wiki/Cementite '''Cementite''' ''(aka '''Iron Carbide''')''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' - really a [https://en.wikipedia.org/wiki/Ceramic '''Ceramic''']. This layered structure is called [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] because of its appearance.

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	When [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] with a very low '''Carbon''' content is '''Quenched''' the resulting '''[[Crystalline Structures\|BCC]]''' structure can accommodate the extra '''Carbon''' atoms and no great distortion takes place so the '''Steel''' is relatively unaffected by this rapid cooling.		=====Tool Steel=====
			[[File:IronCarbonPhaseDiagram.png\|500px\|right\|Iron Carbon Phase Diagram]]

			When [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] with a very low '''Carbon''' content is '''Quenched''' the resulting '''[[Crystalline Structures\|BCC]]''' structure can accommodate the extra '''Carbon''' atoms and no great distortion takes place so the '''Steel''' is relatively unaffected by this rapid cooling. It is for this reason that '''Mild Steel''' cannot be '''[[Heat Treatment\|Hardened and Tempered]]''' but '''Tool Steel''' can.


			<span style="color: green">'''Note:'''
			The approximate, workshop ‘rule of thumb’, '''Carbon''' percentages for '''Mild Steel''' and '''Tool Steel''' are indicated but in reality, there are many much more precise [https://en.wikipedia.org/wiki/SAE_steel_grades '''SAE Grades'''] of [https://en.wikipedia.org/wiki/Carbon_steel '''Carbon Steel'''] available to suit the wide range of applications for this very versatile engineering material.
			</span>


			=====Cast iron=====

			[https://en.wikipedia.org/wiki/Cast_iron '''Cast Iron'''] is an '''[[Alloy]]''' of '''Iron''' and '''Carbon''' which contains more than 2% of '''Carbon'''.


	[[Category:Materials and Components]]		[[Category:Materials and Components]]

DT Online at 19:50, 23 March 2017

2017-03-23T19:50:06Z

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	If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' ~~indeed~~ such that the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.		If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' such that, when a certain percentage of '''Carbon''' is exceeded, the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present, then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.


			When [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] with a very low '''Carbon''' content is '''Quenched''' the resulting '''[[Crystalline Structures\|BCC]]''' structure can accommodate the extra '''Carbon''' atoms and no great distortion takes place so the '''Steel''' is relatively unaffected by this rapid cooling.






	[[Category:Materials and Components]]		[[Category:Materials and Components]]

DT Online at 19:14, 23 March 2017

2017-03-23T19:14:15Z

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	But immediately above 723°C '''Iron''' changes to a different single phase '''[[Crystalline Structures\|FCC]]''' structure called [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] and now can absorb up to about 0.8% carbon - and this increases with rising temperature. [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] can only exist at this elevated temperature and so as it cools all the extra '''Carbon''' has to go somewhere.		But immediately above 723°C '''Iron''' changes to a different single phase '''[[Crystalline Structures\|FCC]]''' structure called [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] and now can absorb up to about 0.8% carbon - and this increases with rising temperature. [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] can only exist at this elevated temperature and so as it cools all the extra '''Carbon''' has to go somewhere.

	----		----
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	</span>		</span>
	----		----
	The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] shows that for '''Steels''' with less than about 0.8% '''Carbon''' the mix solidifies into a two phase structure containing [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] which is very '''[[Hardness\|Soft]]''' and '''[[Ductility\|Ductile]]''', and a layered structure of both [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] and [https://en.wikipedia.org/wiki/Cementite '''Cementite''' ''(aka '''Iron Carbide''')''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' - really a [https://en.wikipedia.org/wiki/Ceramic '''Ceramic''']. This layered structure is called [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] because of its appearance.		The [https://en.wikipedia.org/wiki/Phase_diagram#Binary_phase_diagrams '''Phase Diagram'''] shows that for '''Steels''' with less than about 0.8% '''Carbon''' ''(i.e. Hypo Eutectic Steel)'' the mix solidifies into a two phase structure containing [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] which is very '''[[Hardness\|Soft]]''' and '''[[Ductility\|Ductile]]''', and a layered structure of both [https://en.wikipedia.org/wiki/Ferrite_(iron) '''Ferrite'''] and [https://en.wikipedia.org/wiki/Cementite '''Cementite''' ''(aka '''Iron Carbide''')''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' - really a [https://en.wikipedia.org/wiki/Ceramic '''Ceramic''']. This layered structure is called [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] because of its appearance.


Line 67:		Line 67:


	In '''Steel''' with ~~more than~~ about 0.8% of '''Carbon''' ~~there~~ is ~~too much~~ '''Carbon''' ~~to just form~~ [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] ~~and also, if it~~ is '''~~Quenched~~''' ~~there is no time for it~~ to ~~precipitate out and~~ form [https://en.wikipedia.org/wiki/~~Cementite~~ '''~~Cementite~~''']~~, so the extra remains trapped in~~ a ~~deformed '''[[Crystalline_Structures\|BCC]]''' structure called~~ [https://en.wikipedia.org/wiki/~~Martensite~~ '''~~Martensite~~'''] ~~which is very '''~~[~~[Hardness\|Hard]]~~''' ~~and~~ '''~~[[Brittleness\|Brittle~~]~~]''' indeed such that~~ the ~~'''Quenched''' steel can break like a stick of chalk~~.		'''Steel''' with about 0.8% '''Carbon''' is known as '''Eutectoid Steel''' and at this concentration of '''Carbon''', the grain structure is completely [https://en.wikipedia.org/wiki/Pearlite '''Pearlite''']. In '''Steel''' with more than about 0.8% of '''Carbon''' ''(i.e. Hyper Eutectoid Steel)'' there is too much '''Carbon''' to just form [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] and a mixture of [https://en.wikipedia.org/wiki/Pearlite '''Pearlite'''] with additional [https://en.wikipedia.org/wiki/Cementite '''Cementite'''] precipitating out at the grain boundaries is formed.


	~~The more~~ '''~~Carbon~~''' ''(e.g. ~~up to about 2%)~~'' ~~which is present then~~ the ~~more~~ [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is ~~formed~~. ~~This does not occur in~~ '''~~Low~~ Carbon''' ~~steel~~ ''(e.g. ~~less than 0.5~~%)'' ~~because there~~ is ~~insufficient extra '''Carbon''' to form~~ [https://en.wikipedia.org/wiki/Martensite '''Martensite'''].		If [https://en.wikipedia.org/wiki/Austenite '''Austenite'''] is '''Quenched''' there is no time for the '''Carbon''' to precipitate out and form [https://en.wikipedia.org/wiki/Cementite '''Cementite'''], so the extra remains trapped in a deformed '''[[Crystalline_Structures\|BCC]]''' structure called [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] which is very '''[[Hardness\|Hard]]''' and '''[[Brittleness\|Brittle]]''' indeed such that the '''Quenched''' steel can break like a stick of chalk. The more '''Carbon''' ''(e.g. up to about 2%)'' which is present then the more [https://en.wikipedia.org/wiki/Martensite '''Martensite'''] is formed.



	[[Category:Materials and Components]]		[[Category:Materials and Components]]