Quench severities
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
Example quench design problems What quench should be used for 2" diam. 4140 bar to full harden 1/2" deep? Quench severity ≈ 1.25 Water quench w/some agitation 6
Example quench design problems Quench severity ≈ 1.25. What is hardness at center? 7
Example quench design problems Quench severity ≈ 1.25. What is hardness at center? 2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈ 53 Jominy curve 7
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)
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
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
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
Result: the galvanic series Corrosion more cathodic more anodic Result: the galvanic series anode cathode electrolyte electrical connection electrolyte electrical connection Zn Cu
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
What constitutes an anode/cathode pair? Corrosion What constitutes an anode/cathode pair? Dissimilar metals 1 2 Practical example: crevice corrosion Different electrolytes
What constitutes an anode/cathode pair? Corrosion What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes 1 2 Deformation ––> non-homogeneous residual stress
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
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
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)
Corrosion Then what about micro cells? anode & cathode within single material operating on a micro scale Segregation (coring)