Heat input and cooling rate

[nabeel3]

Dear All,

I am a student of Welding. I couldn’t understand the reason for the below statement.
“For high heat input the cooling rate is low and for low heat input the cooling rate is high.”
As far as I know the rate of cooling depends on the temperature difference. High heat input should result in high temperature than low heat input and the temp differential should be high in high heat input. Hence the cooling rate should be high in high heat input case.

 

[dauwerda]

High heat input results in the base metal heating more, therefore it will take much longer for the base metal to return to ambient temperature (cooling rate is low). If the weld were made with low heat input, the base metal does not heat up as much, and therefore returns to ambient temperature quickly (cooling rate is high).

High heat input and low heat input are not referring to the maximum temperature achieved, rather they are referring to how much heat is absorbed by the base metal. A good comparison would be a full cup of coffee vs a half cup of coffee left at ambient temperature, the full cup will take longer to cool down than the half cup.

 

[nabeel3]

Thank you,