HOW to read a hardness value on ITT curve ?

[stanislasdz]

Please what is the value of this hardness ?
How to read value on ITT curves ?

 

[metengr]

stanislasdz;
Normally, if hardness data is reported it would be provided for CCT (continuous cooling transformation) diagrams on the abscissa versus TTT diagrams. The reason is that the hardness will vary as a function of cooling rate, which is more appropriate for CCT diagrams.

The hardness data reported on the ordinate in the above TTT diagram may be after complete transformation has occurred at ambient temperature for this material. I would suspect the hardness data was added in the text where this TTT diagram was referenced.

 

[CoryPad]

How accurate do you need this to be? You can extrapolate based upon the positions of 27,5 HRC and 90 HRB. I would estimate this to be close to 100 HRB = 20 HRC.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[arunmrao]

This is a superimposition of hardness data on TTT curve. As CoryPad has suggested the only way to obtain is by extrapolation. Also as it is a semilog representation ,I would say it is 22-23 HRC .



" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[metengr]

As I suspected, you would have various answers. In my opinion, the only correct response, given the information you provided, is the range below;

Hardness range between 95HRb to 27 HRc.

 

[stanislasdz]

Thanks for all !!

In fact i need to know what is the Hardness of this alloy after tempering at 550°C during 6 hours.

Is it the correct way to use TTT Curve ?

 

[metengr]

stanislasdz;
The above posts adequately explain how to use the hardness scale superimposed on the above TTT diagram. The TTT diagram and superimposed hardness scales, however, should not be used for determining hardness after tempering.

A 6 hour tempering duration requires actual hardness testing. Most tempering charts for steels provide hardness data after tempering only 1 hour at temperature. Your only other option is to calculate a tempering parameter from known hardness data (a graph of hardness versus tempering temperature) and use the relationship similar to the Larson Miller parameter, where the hardness is a function of tempering time and temperature.