Heat input and cooling

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Student

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Apr 19, 2020, 1:00:59 AM4/19/20
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Dear all
I am confused about the following statement. Can anyone tell me the reason.

High heat input causes slow cooling and low heat input causes fast cooling.

I understand that cooling is a function of temperature differences between the metal and ambulance system. If high heat input causes high temperature then temperature differential should be higher than low heat input.
Can any one tell me the reason.

james gerald

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Apr 19, 2020, 1:39:29 AM4/19/20
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High Heat Input reduces the Cooling rate as the Peak temperatures experienced from the weld zone is wider, moreover thermal conductivity remains same and it varies based on critical thicknesss as it changes from 2 Dimensional flow to 3 Dimensional flow as thickness is increased. That is the reason why Preheating  is done for thicker steels to reduce the cooling rate.

Cooling Rate Formula for 3D Flow.

Inline image
You will also note from the above Formula That Cooling Rate R is inversely proportional to Heat Input Hnet.

Please also find below the Cooling Rate formula for 2 Dimensional Flow.

Inline image


Above formulas from AWS Handbook.

Thanks & Regards

J.Gerald Jayakumar




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Kannayeram Gnanapandithan

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Apr 19, 2020, 1:53:40 AM4/19/20
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Yes. More heat input will be cooled slowly depending on somany condition where as less heat input will be cooled faster . 

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George Dilintas

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Apr 19, 2020, 11:21:43 AM4/19/20
to Kannayeram Gnanapandithan, material...@googlegroups.com
The issue is complex. 
Higher heat input  with high sink (large and thick work) will result in high cooling rate which will result to high hardness if no adequate preheat

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-------- Αρχικό μήνυμα --------
Από: Kannayeram Gnanapandithan <kgpan...@gmail.com>
Ημερομηνία: Κυρ, 19 Απρ 2020, 08:48
Προς: materials-welding <material...@googlegroups.com>
Θέμα: Re: [MW:30797] Heat input and cooling
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