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Quench severities
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Example quench design problems
What is max bar size for 4140 which will full harden with quench severity of 0.35? Jominy curve 6 6
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Example quench design problems
What quench should be used for 2" diam bar to full harden 1/2" deep? Quench severity ≈ 1.25 Water quench w/some agitation 6
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Example quench design problems
Quench severity ≈ What is hardness at center? 7
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Example quench design problems
Quench severity ≈ What is hardness at center? 2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈ 53 Jominy curve 7
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Corrosion Hint for exams (and life): A substance which is corrosive will corrode other substances SS is thus certainly non-corrosive But it is also non-corrodable (in most instances)
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Most corrosion is electrochemical
Galvanic cell is necessary electrolyte electrical connection No corrosion if one of these is missing: anode cathode electrolyte electrical connection anode cathode
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Most corrosion is electrochemical
Galvanic cell is necessary electrolyte electrical connection Corrosion at anode Me = Me+n + ne– (metal dissolves) anode cathode No dissolution at cathode
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What constitutes an anode/cathode pair?
Corrosion What constitutes an anode/cathode pair? Dissimilar metals Zn Cu Ex: Cu & Zn (Zn corrodes) electrolyte electrical connection How do we know? Many combos tried experimentally
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Result: the galvanic series
Corrosion more cathodic more anodic Result: the galvanic series anode cathode electrolyte electrical connection electrolyte electrical connection Zn Cu
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What constitutes an anode/cathode pair?
Corrosion What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes 1 2 Ex: 1 contains little dissolved oxygen 2 contains much dissolved oxygen
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What constitutes an anode/cathode pair?
Corrosion What constitutes an anode/cathode pair? Dissimilar metals 1 2 Practical example: crevice corrosion Different electrolytes
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What constitutes an anode/cathode pair?
Corrosion What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes 1 2 Deformation ––> non-homogeneous residual stress
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What constitutes an anode/cathode pair?
Corrosion What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes 1 2 Deformation ––> non-homogeneous residual stress Non-passivated vs. passivated metal or alloy
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Corrosion What constitutes an anode/cathode pair? In summary– Anything that makes two half-cells different gives anode & cathode ––> corrosion We can call these types macro cells
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Corrosion Then what about micro cells? anode & cathode within single material operating on a micro scale Grain boundary - high energy region…anodic wrt bulk of grain Differently oriented grains - some planes of atoms dissolve faster than others Segregation (coring)
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Corrosion Then what about micro cells? anode & cathode within single material operating on a micro scale Segregation (coring)
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