Iron crystal structures

when a molten metal solidifies the atoms arrange themselves into definite patterns called crystal structures the two most common crystal structures and metals are body centered cubic and face centered cubic these crystal structures grow uniformly in all directions within each developing crystal as the metal cools these crystals are confined by the adjacent developing crystals forming grains the line of intersection between grains is called a grain boundary because the grains form independently their crystal structures developed tilted in various directions.
                       all atoms in these crystalline structures are held in place by electromagnetic attraction to neighboring atoms if a force or load is applied to a metal these electromagnetic bond stretch allowing the atoms to move slightly when the load is removed the bonds pull the atoms back into position if the applied for succeeds the metals yield strength those electromagnetic bonds will break causing permanent stretching or deformation.
                    this diagram is the iron carbon phase diagram let's examine how temperature and carbon content combine to provide a variety of metallurgical structures the left-hand side of this diagram is ferrite. ferrite is iron containing an extremely minute amount of carbon at room temperature fair itis magnetic relatively soft and has a body centered cubic crystal structure at room temperature the solid solubility or the amount of carbon that can be dissolved in ferrite is practically zero the amount of carbon dissolvable in ferrite increases to only a maximum of point zero two five percent at one thousand three hundred thirty three degrees fahrenheit.
                    when heated to one thousand six hundred seventy degrees fahrenheit fair rights body centered cubic crystal structure rearrange is itself into a face centered cubic structure known as austenite.this transformation to boss tonight is an important phase in the heat treatment of steals .
                      austenite crystal structure allows it to absorb up two point eight zero percent of carbon at one thousand three hundred thirty three degrees fahrenheit increasing to a maximum of two point zero percent at two thousand sixty six degrees fahrenheit the right-hand side of this iron carbon phase diagram represents cementite also known as iron carbide.
                          cementite contains six point six seven percent carbon though this phase diagram ranges from ferrite with very low carbon content to cementite with six point six seven percent carbon most steals contain less than to point zero percent carbon the carbon content is the major factor in determining the properties that can be developed in steel the use of very low carbon contents or very high carbon contents provides many different steel compositions with very different properties for this reason steel is suited to a wide range of engineering applications.
                           let's take a closer look at some examples of how carbon affects the hardness of steals if steel containing point zero three zero percent carbon is heated to about one thousand seven hundred degrees fahrenheit the structure will consist entirely of austenite if it is then cooled slowly at about one thousand six hundred fifty degrees fahrenheit the austenite begins to transform tu ferrite as cooling continues more and more ferrite is for me until it one thousand three hundred thirty three degrees fahrenheit the remaining austenite transforms completely ferrite can retain only point zero two five percent carbon at this temperature so to accommodate the carbon in access of this amount the remaining austenite transforms to a mixture aferrite and cement ait in alternating thin plate like lawyers this structure is referred to as per light at room temperature the steel is mostly ferrite with patches of pro-life


+ comments + 1 comments

November 15, 2012 at 11:40 AM

good job

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