Steel_Part_2

Steel_Part_2 - Steels Part 2 Non-equilibrium Processing of...

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Steels Part 2.
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Non-equilibrium Processing of Steel: For simplicity -- Consider a 0.77 C steel Equilibrium cooling yields 100% coarse pearlite Progressively faster cooling yields finer and finer pearlite which is progressively stronger
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Now consider an extreme nonequilibrium condition—hot FCC austenite immersed directly into liquid nitrogen γ 0.77%C wants to change crystal structure to form the BCC structure BCC however, can only hold 0.02% C Carbon has insufficient time to diffuse The material ends up with a body-centered structure containing 0.77% C (~40x equilibrium) Result is grossly distorted BCC structure (actually BCT or body-centered-tetragonal) called Martensite(Marten’s structure)
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In summary: Now -- Consider the following experimental arrangement γ 0.77C equilibrium cool Pearlite ( α + Fe 3 C) γ 0.77C liquid N 2 Martensite 0.77C (BCT) Furnace T>A 1 Molten Salt T<A 1 Liq N 2
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Begin by heating foil specimens to the austenitizing temperature At time zero, a trap door opens in the bottom of the furnace and foil specimens drop into the molten salt Because of specimen geometry, their temperature instantaneously adjusts to that of the molten salt After specified increments of time, (1 sec, 5
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This note was uploaded on 05/20/2008 for the course MET 121 taught by Professor Kohser during the Spring '07 term at Missouri S&T.

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Steel_Part_2 - Steels Part 2 Non-equilibrium Processing of...

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