lecture 15 - Lecture 15 Heat Treat / Precipitation...

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Unformatted text preview: Lecture 15 Heat Treat / Precipitation Hardening Stephen D. Downing Mechanical Science and Engineering 2001 - 2010 University of Illinois Board of Trustees, All Rights Reserved ME 330 Engineering Materials ME 330 - Lecture 15 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 1 of 22 This Lecture ... Hardenability of Steel Review Heat Treatment Review Precipitation Hardening Introduction to Fracture ME 330 - Lecture 15 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 2 of 22 Hardness vs. Hardenability Hardness resistance to deformation Hardenability ability to be form martensite (to be hardened) Formal definition: Hardenability ability of an alloy to be hardened by formation of martensite due to given heat treatment High hardenability martensite forms (i.e. hardens) far into specimen, not just at surface Hardenability ME 330 - Lecture 15 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 3 of 22 Jominy End Quench Test Standard test for measuring hardness of any material Sample of fixed geometry suspended over water jet Geometric factors all constant Only effect on hardness is alloying content Hardness measured as function of distance from quenched end Hardness, HRC Distance from quenched end Cooling rate Distance ME 330 - Lecture 15 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 4 of 22 Annealing- Heat, holding at temperature, gradual cool General term, but also used for specific processes Tempering-Heat martensite to get diffusional transformation: martensite (BCT single phase) tempered martensite ( + Fe 3 C) Still have ultra-fine microstructure, but more ductile Process annealing-Reverse effects of cold work; recovery, recrystallization, but little grain growth Stress relief- Lower temperature anneal to undo thermal stress or transformation mismatch stress Spheroidizing- Heat pearlite just below eutectoid temp to produce spheroidal structure; makes steel easier to machine Review: Heat Treatment of Steel ME 330 - Lecture 15 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 5 of 22 Heat Treatments Full Annealing Heat to 15-40 C above phase transition line, hold for diffusion, and slow cool (usually in a furnace, often takes number of hours). Returns microstructure to coarse pearlite. Often performed on steels to be machined or formed to increase ductility Normalizing Heat to the fully austenite region and air cool....
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lecture 15 - Lecture 15 Heat Treat / Precipitation...

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