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CARBON STEEL Microstructure & Mechanical properties

CARBON STEEL Microstructure & Mechanical properties. EXPERIMENT # 10 Instructor: M.Yaqub. TYPE OF IRON. a- Iron (Ferrite) Stable up to 912 o C. BCC in Structure. Soft in pure state. Can disolve up to .02% Carbon. g- Iron (Austenite) Stable between 912 o C and 1394 o C.

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CARBON STEEL Microstructure & Mechanical properties

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  1. CARBON STEELMicrostructure &Mechanical properties EXPERIMENT # 10 Instructor: M.Yaqub

  2. TYPE OF IRON • a-Iron (Ferrite) Stable up to 912 oC. • BCC in Structure. Soft in pure state. • Can disolve up to .02% Carbon. • g-Iron (Austenite)Stable between 912 oC and 1394oC. • FCC in Structure • Cementite (Iron Carbide) Fe3C Hard and Brittle • Complex Structure.

  3. TYPE OF STEEL • Hypo-Eutectoid Steel:% of Carbon < 0.7 • Eutectoid Steel:% of Carbon = 0.7 • Hyper-Eutectoid Steel:% of Carbon > 0.7

  4. LOWER CRITICAL TEMPERATURE When steel heated, microstructure changes (new grains forms). The temperature where this growth starts is called Lower Critical Temperature, fix for all % of C, 727oC

  5. UPPER CRITICAL TEMPERATURE • The temperature where new grains formation completes, (All old grains replaced by new grains) is called Upper critical temperature. • This temperature depends upon % of Carbon in steel. • Can be taken from Iron-Carbon Diagram .

  6. IRON-CARBON DIAGRAM

  7. HEAT TREATMENT PROCESSES

  8. ANNLEALING • Heating the steel above upper critical temperature and then cool in furnace (very slow cooling, cooling rate 10 oC / hour). • Annealing reduces the hardness and improve ductility. • Structure after annealing is coarse pearlite.

  9. NORMALIZING • Heating the steel above upper critical temperature and then cool in air (cooling rate 100 oC / hour). • Structure after normalizing is fine pearlite. • Hardness more than the Anealed steel.

  10. QUENCHING • Heating the steel above upper critical temperature and then cool in water or in oil (very fast cooling). • After quenching, steel is very hard and brittle and practically no use. • Structure after quenching is fine martensite which is complex, hard and brittle structure. .

  11. TEMERING • Reheat the quenched steel up to intermediate temperature (below lower critical temperature) and then cool. • The structure is called tempered martensite. • After tempering, steel become tough and looses some hardness. It become use able now.

  12. SUMMARY

  13. PEARLITE • A homogenous mixture of Cementite Fe3C and a-Iron in solid state. • For Hypo Eutectoid steel, final structure is Ferrite (a-Iron) and pearlite.

  14. PEARLITE (Cont’d.) • For Hyper Eutectoid steel, final structure is cementite and pearlite.

  15. PEARLITE (Cont’d.) • For Eutectoid steel, final structure is only pearlite.

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