Limesh
Simple rule: you will have no phase changes unless the steel is heated above the lower critical temperature (LCT).
If you have an alloy steel, the lower critical temperature will be different than for a carbon steel, but the above rule applies.
If the maximum temperature is below the lower critical, there will be no phase change but coarsening of pearlite will occur. Other structural changes may occur but the phases will not be effected (creation of tempered martensite or bainite, redistribution of stresses, creep due to stress relief etc.).
The major reason heating and cooling rates are restricted are to prevent the creation of residual stresses usually caused by uneven distribution of heating/heat removal . These stresses can cause cracking, particularly in highly restrained structures.
{Note with regard to the simple rule above, there will be an apparent upward shift in LCT with increasing heating rate (diffusion controlled process) with respect to the equilibrium LCT. Similarly, there will be an apparent downward shift in the upper critical temperature (UCT) for diffusion dependent processes with respect to the equilibrium UCT.}
Any further questions, please append.
John A. Henning
Senior Engineer, Welding & Materials
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of limesh M
Sent: Monday, September 26, 2011 1:59 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:12534] Uncontrolled heating and cooling effect of Carbon steel below lower critical temperature
Mr. Muthu Bharathy,
These phenomena has already been proved well before by scientists.These things are well explained by authors like Sidney H. Avner,George E. Dieter,Sir Allen Cottrel,William D. Callister,Herman W.Pollack etc. in their material science and metallurgy books.Because Austenite is the one plays a major role to form other phases or micro structure during cooling(Cooling rate has great significance in getting coarse or fine grained micro structure).For example,without austenite ,there is no martensite formation in carbon steel during rapid cooling(quenching) from above upper transformation temperature due to lattice shear(no time for diffusion) and I don't think that martensite simply exists as it is.These phenomena is well explained in CCT and TTT diagrams.If you have any different opinion or my understanding is wrong ,you are most welcome to explain it as I don't have much expertise in material science.Moreover, my query was about the phase changes with in the limit of lower critical temperature of Iron-Iron carbon equilibrium diagram during uncontrolled heating and cooling.
Furthermore,I didn't get what do you mean by 'prove' since I didn't claim any kind of invention in my query!!
Regards,
Limesh
On Sun, Sep 25, 2011 at 2:41 PM, muthu barathi <muthu_barathi@rediffmail.com> wrote:
Dear Sir,
Better you may make a trial experiment and prove it.
Thanking You,
Honesty is the best Policy
With Warm Regards,
Muthu Barathi P
Mobile No:00962788269821 (Jordan)
00962775401951
From: limesh M <limesh78@gmail.com>
Sent: Sun, 25 Sep 2011 12:53:25
To: materials-welding@googlegroups.com
Subject: Re: [MW:12515] Uncontrolled heating and cooling effect of Carbon steel below lower critical temperature
Dear Mr. Biplab,
As per my understanding,TTT (C-Curve)or CCT won't give any idea on my query.Both diagrams discussing about the phase changes occurs on cooling above upper transformation temperature.So,CCT or TTT gives information on austenite decomposition.For a hypothetical manner we can say above lower critical temperature on hypo-eutectoid steel as it contains partial gamma iron(austenite) and alpha iron(ferrite).
Regards,
Limesh
On Mon, Aug 22, 2011 at 4:12 PM, Biplab Pal <biplab.mech@googlemail.com> wrote:
You should go through TTT diagram.
On Sun, Aug 21, 2011 at 7:48 PM, limesh M <limesh78@gmail.com> wrote:
Dear All,
Material : Carbon steels in between 0.008% carbon and 6.67 % carbon.
1.Is there any metallurgical changes(phase change) will occur other than pearlite,if I heat rapidly uncontrolled heating)low carbon steel just below or equal to lower critical temperature(723 C) as per iron-carbon equilibrium diagram?
2.1.Is there any metallurgical changes(phase change) will occur other than pearlite,if I cool rapidly (uncontrolled cooling, no quenching by any kind of liquid medium)low carbon steel from just below or equal to lower critical temperature(723 C) as per iron-carbon equilibrium diagram?
Regards,
Limesh--
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Thanks & Regards
Biplab Pal
Industrial Services, Inspection Engineer.
SGS India Pvt. Ltd.
Kolkata Branch
E-mail: biplab.mech@gmail.com
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