ASTM A352 Grade LCB Heat Treatment Recommendation 3

[mahadhatu]

What is the recommended heat treatment for ASTM A352 Grade LCB Steel to meet the impact testing requirements?

So far I have tried a few heat treatment cycles. Normalized at 1625F and tempered at 1125. Double Normalized at 1625F and tempered at 1125F, water quenched from 1625F and tempered at 1125F. The maximum value I got was 8 ft-lb in the Q and T condition which does not meet the minimum requirement.

Chemistry is
C 0.25, Si - 0.45, Mn - 0.96, S - 0.012, P - 0.018, Cr - 0.42

Any helpful tips would be greatly appreciated.

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There is always some thing better out there...
Mahadhatu

 

[TVP]

Have you evaluated the prior austenite grain size after heat treating? Fine grain size is needed to obtain good toughness. ASTM number 5 or finer is the usual starting point for good toughness.

 

[mahadhatu]

No Sir.. I have not checked the grain size after heat treatment.
I am not sure whether my selection of Normalizing temperature is correct considering the presence of Chromium ( 0.42).
I also found that the impact property was the same regardless if the steel was tempered after Normalizing.

--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[arunmrao]

You must normalize and double temper the casting to get your impact property value. Also reduce Carbon to 0.22%, small amount of Ni or Mo will help in getting consistent impact values. Hope it helps.

 

[mahadhatu]

Thank you, arunmrao.. What tempering temperatures would you suggest ?

--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[arunmrao]

Search this forum and you will find a number of good recommendations. Hope you get the solution.

 

[metengr]

Your chemistry range is well within the specification necessary to achieve 15 ft-lbs min at -50 deg F for Grade LCB. Per ASTM A 352 LCB; heat treatment should consist of the following;

Austenitize
Liquid Quench (this is in the material specification for ferritic materials for thicker castings) or normalize.
Temper at 1100 deg F minimum.

I would suspect your section thickness of the casting requires liquid quenching or faster cooling if normalizing.

 

[jwhit]

Many foundries use the following cycles: Normalize 1725F air cool, Austenitize & water quench from 1650F, temper at 1250F air cool(all+/-25F). With good clean low P & S material you should end up at 25FTlbs or better. I've seen LCB go over 60 Ft lbs out of an AOD. Clean metal is the other key to good LCA/B/C. In regards to your chemistry, having the Mn on the high side is good, I'd prefer to see less Cr (<0.25). A touch of residual Ni can be beneficial but isn't necessary to meet the minimum requirement.

 

[weldstan]

It was made with fine grain melting technique, I assume? What's the Al content? Suggest increasing the Mn:C ratio and lowering the Chromium to residual.

 

[mahadhatu]

UPDATE:

Thank you every one for your input and help.

Arunmrao: We did not have a choice to change chemistry on this part. I heat treated one of the test bars with your recommendation of a double temper and got a 3ft-lb value at minus 50 deg F.

Metengr: I did not get a value higher than 3ft-lbs with your recommended heat treatment cycles. The part in question has a maximum wall thickness of 3". I was performing tests on test bars from the same heat that I had cast for testing purposes. I tried liquid quench as well but with no improvement in the impact values.

Jwhit: Your recommendation of the higher temperature homogenize worked along with the normalize - quench and temper. I heat treated 3 test bars out of the same heat as follows and got the following results:

1750F - 2h - Air Cool; 1650F - 2h - Water quench - 1250F 6h Air Cool - 15ft-lb at minus 50 deg F
1750F - 2h - Air Cool; 1650F - 2h - Oil quench - 1250F 6h Air Cool - 12ft-lb at minus 50 deg F
1750F - 2h - Air Cool; 1650F - 2h - Air quench - 1250F 6h Air Cool - 8ft-lb at minus 50 deg F

I did not measure the grain size on any of these test bar samples but I believe our initial casting had large grain size leading to lower impact properties. The initial homogenize cycle helped reduce this grain size just enough to push the impact value over the minimum values with liquid quench but not with air quench.

I am assuming though that if I had the right chemistry and had used the correct grain refiners during casting we would be able to exceed the impact values with a normalize and temper heat treatment cycle only without any of the above extensive cycles.

Again, Thanks for all of your help.


--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[TOVmania]

I think it is the purity that is the concern. Like jwhit commented, C & Cr & P & S should be reduced and Mn & Ni should be maximized as much as possible within ASTM chemical specification. Normal LCB.LCC impact results are around 30~35 ft.lb at -50F if properly manufactured. Impact results from base metal section of welded AOD materials after stress relieving from tempering have yielded over the double of what jwhit stated at -50F from a thrid party accredited laboratory.