mp4f01- MAT ENGINEERING

future MAE students pls do not take F01 as ur PE UNLESS u r crazily in love with Material Engineering. =)

Chap 7: Review of steel

4 types of corrosion:
1) Galvanic corrision
-occurs when 2 metal or alloys having diff composition electrically coupled

2)Pitting
-holes form

3)Stress corrossion cracking (SCC)
-combination of tensile stress and particular type of corrision enmt

4) Intergranular Corrision
-solute atoms segregate to the grain boundaries
-auste&ferri IG corr: segregation of C to the grain boundaries
- Cr depletion--->senstized

How to protect stainless steel fr IG corr.?
1) Heat treament to dissolve cr carbides
2)lower C below 0.03%
3)allow stainless steels with Nb or Ti to form carbides--->Cr remian in soln

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1)HSLA- low alloy
2) Tool Steel - High alloy
3) stainless S. - high alloy

alloying elements added for:
1)to increase strength
-sss
-ppc hrdening
-refine grain size

2)improve hardenability
-to incrse depth

3)to give corr resist.
-stainless steeel: cr

4)gve special properties
-add mo,v,w

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R efining grain Sizr:
-increase the yield stress
-increase toughness
-reduction in creep resistance

7.3 driving force for microstructual chges
3 basic concepts:
a)there must be driving force for changes to occur
b)a route that process can follow
c)driving force means: work or energy ====== Wf = mgh (decrease of potential energy)

Driving force for grain growth:
-grain boundary energy tied up in a polycrystalline material works to give a driving force for grain coarsening.

Driving force for ppl coarsening:
-many steels dpend for their strength on a dispersion of fine 2nd-phase particles (ppc hdning)

*during coarsening small ppc shrink; large ppc grow at the expense of the small ppc. #diffusion#

#Shapes of ppc:

-when boundary energy is the dominant factor-shape of ppc is SPHERICAL.

*structual change:
mechsm of the transformation will affect the shapes. eg, eutectoid reaction.

*nucleatiom in steels:
-in steels, new phase usually HETEROGENUOUSLY ON HIGH ENERGY DEFECTS.
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