DI Calculations for Higher C Steel

[bovs7]

Hi,

I've been trying to use ASTM A255 to try and calculate DI values and ultimately theoretical hardness profile for a new trial steel grade we are sourcing to make parts of up to 125 mm diameter.

Problem is the new steel grade is 1% C. ASTM only designates for up to 0.7% C... I've tried extrapolating the equations and applying to our higher C chemistry but my results don't seem to match practical observations.

So... 3 questions!
Is there a reason the Grossmann method can only be applied up to 0.7% C?
Is there a similar limit on chemistries in terms of relating Jominy tests to actual hardness penetration?
Is there an alternative calculation that can be applied to higher C steels?



Thanks for any help from a frequent-reader-first-time-poster!

 

[dbooker630]

Table A2 in SAE J406 shows the original Grossman factors up to 0.90% C. That is the highest I have seen.

 

[yudhichen]

Dear boys7,

if i may to add (and discuss as well), i wonder why you keep calculating DI value.
last time i studied this grossman and i found this is old method that everybody not use anymore (i suppose).
i made some posting on my blog regarding how to find hardness profile based on jominy test data.
hope this helps

http://yudhichen.wordpress.com/2014/03/22/alloy-steel-hardenability-for-wellhead-equipments/

 

[bovs7]

Thanks for the interesting link.

The reason I am using Grossman calculations is that I am trying to assess theoretical hardness profiles for given chemistries. In particular, I am trying to demonstrate that a potential material for our part will, even at its minimum chemistry, give us a better hardness profile than the current material being used (for which we have Jominy data).

The problem is my calculated theoretical Jominy profile using Grossman does not match the actual data. The Jominy data itself is suspicious, but I cannot question it with my calc since technically we are working above 0.90%C so my calculation is not valid.

I also suspect that we may incorrectly make our material choice based on a one-off test of an actual sample material without considering whether the full chemical range of the specified grade will provide us the same required result.

 

[metengr]

C.F. Jatczak, Hardenability Calculation of Hardenability in High-Carbon Steels, Steel Heat Treating Fundamentals and Processes. Vol 4A, ASM Handbook, ASM International, 2013, p 80–88.

 

[bovs7]

Hi metengr thanks for the reference!

I have finally traced it down and it's very helpful. I do have one question still though.

The article talks about the prior normalisation or quench temperature as determining the hardenability factors. I haven't quite understood however if this is specifically a reference to a normalising treatment prior to heating for quenching, or if it is a reference to the temperature from which you quench.

Our current practice is to forge at a high temperature (approx. 1000 degC) and then cool to somewhere around 800 degC before quenching. Will the 1000 degC affect hardenability? Is the 800 degC the temperature from which we can determine hardenability? Or is the prior condition of the steel before our treatment the main factor?

 

[metengr]

The article talks about the prior normalization or quench temperature as determining the hardenability factors. I haven't quite understood however if this is specifically a reference to a normalizing treatment prior to heating for quenching, or if it is a reference to the temperature from which you quench.

The normalization referred to is treatment performed before austenitizing and quenching.