Lab 1 helps create a better understand of the changes in crystal structures when the annealing and quenching process is applied to 1020 and 1080 steel. The numbered steel refers to the ASTM grain-size number. Formula 1 is used to solve for the grain size. n=2^(G-1) Equation (1) at 100x magnification
Crystal structures change shapes which changes the strength of the material and its properties. The metal might become soft, brittle, hard, or ductile. The four test specimens are all made from cold drawn steel. When steel is cold drawn, the crystal structure changes and creates stress. The stress in the grains can be reduced by the process of annealing. Quenching creates small stresses because carbon does not have time to escape. The annealing process is when
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Creating larger grain boundaries makes the steel more ductile due to there being less paths for dislocations on the boundaries. The grain boundaries are caused by a dislocation. When there is an extra plane of atoms, or a plane of missing atoms, a gap is created causing the grain boundaries. Pearlite, as shown in figure 1 picture B, is caused when the steel is annealed. Pearlite has multiple layers that consist of ferrite and cementite. Ferrite is has a crystalline structure known as a Body Centered Cubic structure. Ferrite is a ceramic compound that has very little carbon causing it to be soft and ductile. Cementite is also a ceramic that has more carbon than ferrite. Quenching a metal is slightly different than annealing. When the steel is heated up, the steel is then rapidly cooled down is water or oil. When the steel is quenched, the heat energy within the center of the part is pulled out quickly. The process of cooling rapidly cooling down the steel creates lots of tinny grain boundaries on the surface. The small grain boundaries are called martensite, as seen in figure 1 picture C. Martensite is a very hard microstructure due to having a dense amount of grain boundaries. The martensite crystals