The famous law in heat Treatment : 1 hour per Inch

[stanislasdz]

In heat tretament there is a famous law : the time of treatment is 1 hour per inch

1- What is the origin of this law ?

2- Is it for Thermal diffusion or for chemical diffusion ?

Stanislastment

 

[swall]

This "rule of thumb" is mainly for thermal diffusion, as the formation of austenite is fairly rapid once temperature is achieved. The only other consideration would be in highly alloyed steels where additional time would be needed to fully dissolve the carbides.

 

[stanislasdz]

Hi swall

Ok but :

What about the macroségrégation or the microségrégation ?

What about also the homogeineization of the grain size ?

 

[swall]

If you are working with castings, yes, longer times might be required to handle the segregation. It all depends on the material and the specs you are working to. Sometimes a homogenization treatment is required; sometimes not.

 

[metengr]

In heat tretament there is a famous law : the time of treatment is 1 hour per inch

1- What is the origin of this law ?

The "rule of thumb" mentioned by swall above was developed based on practical experience in heat treatment shops. It was discovered that holding an item using time at temperature assures adequate soak time to avoid thermal gradients, and to assure complete austenite transformation.

Keep in mind this "rule of thumb" was also developed for post weld heat treatment, and that beyond a certain component thickness (2"), the temperature soak time can be revised to 15 minute increments at temperature.

 

[Yallapragada1022]

As metengr said, it was developed based on practical experience. You can insert thermocouples in your part and figure out how much time it takes for surface and core to reach the temperature also. You would not go wrong with using the rule of thumb.

Rao Yallapragada

 

[stanislasdz]

thanks metengr & Rao...