Silicon content in 4370 Investment Castings

[mewhg]

We use some small 4370 investment castings that have been having problems with non-metallic inclusions. The foundry wants to raise the silicon content from 0.3% to 1.0% in an effort to help with the inclusions.

What would be the effect in raising the silicon content?

The castings are heat treated to 60 HRC and are subject to impact and wear during service.

TIA

 

[arunmrao]

0.3-1.0% is a big jump. Not sure how increase in Si content is going to reduce inclusion defects. Are these inclusions micro or macro in nature? There could possibly be other sources for inclusions to occur. High Si is not desirable as it can affect the impact properties as well interfere in hardening process.

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[mewhg]

They are macro inclusions.....you can see them by eye with no magnification.

They are showing up in a WEDM step. The wire deflects around the inclusions.

I am not getting very good help from the foundry........they have been doing these castings for 5 years without trouble. Now there is an issue and they do not want to look at their process........

 

[arunmrao]

I am providing a few references for further reading. however, if it is macro defect I feel that the problem lies with process controls and chemistry might have no major role to play.

http://neon.mems.cmu.edu/afs/afs2/intro.html

http://www.p2pays.org/ref/08/07546.pdf

Castings : Author John Campbell isbn=0750647906

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[EdStainless]

They may be thinking that if they increase Si and fluidity then these will float out better.
You need to get these guys to keep them out in the first place. My hunch is that it is related to the raw material supply.

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[mewhg]

I know they do not use ignot but create their melt from low carbon scrap sheet metal punchings, pellets of chromium, nickel, moly etc.

I think this is how they can offer us 4370. Its really a non-standard alloy. We may have to switch foundries and use S7 but I don't think S7 can be hardened to 60 HRC with a decent temper.

When I say you can see the inclusions with the naked eye.....some of them are easily 1mm.

 

[metengr]

I think arunmrao is spot on. Inclusions typically are process-related problems from my expierence in visiting various mills, and foundries.

 

[redpicker]

Can you run an X-Ray microprobe analysis on the inclusions to determine their composition? That might help.

I'd ask the foundry what the intent of the Si additions would be and why they feel it would solve the problem. They may actually know more than someone on an internet message board.

I am not sure I agree with arunmrao that the increased silicon will be detrimental. AMS 6257 (300M) is a modified 4340 (with 0.35-0.45 Mo, 1.45-1.80 Si and 0.05-0.10 V) and is used in applications where higher strength and toughness than can be obtained with 4340 is needed. I'm not saying that for your application that the higher Si content would be beneficial, but rather that there are cases where higher Si is used successfully.

rp

 

[arunmrao]

redpicker,
High Si content causing brittleness is a practical observation made. Instead of using steel scrap there was a mixup and high silicon steel was used instead. The castings were found to break like biscuits .

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[CoryPad]

4340 and a casting with 1 % Si is not a fair comparison. The 4340 has been homogenized and hot wrought, which provides a ductile structure. An as-cast steel with 0.7 (!) % C and 1 % Si is going to have ductility problems.

Regards,

Cory

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

 

[redpicker]

I'm not saying that the proposed modification will be accepatble or not, only that I would not condem the silicon additon of 1% flat out. There are examples of high strength steels with much higher silicon contents that exhibit toughness levels suitable for aircraft applications. I am not trying to argue with arunmrao, only to point out that higher silicon does not always mean unacceptable toughness levels.

Cory, I was not trying to compare 4340 to a casting with 1% Si (I agree, that would be an unfair comparison). I was comparing 4340 to 300M, where one of the major differences is a 5 to 6 times increase in the silicon content. That is, to provide an example where the higher silicon content does not result in unacceptable toughness. Are you trying to say that an as-cast steel with 0.7 % C and 0.3% silicon will not have "ductility problems"?

My advice to the OP was that if he had questions on what the vendor proposed, to dicuss it with them. Most likely, this isn't the first time they have run across this problem and they might have some practical experience in the matter. As to what the effect of raising the silicon content in the material would be, they might just be able to answer that, too.

rp

 

[CoryPad]

I confused this issue by mentioning 4340 - I meant 300M.

I think an as-cast steel with 1 % Si will have worse ductility than if it had 0.3 % Si.

I think you are giving the vendor too much credit - this is a HUGE change that is proposed, and if the casting contains 1 mm sized inclusions, then there is a fundamental problem with the entire process.

Regards,

Cory

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

 

[mewhg]

Redpicker,

I have discussed this with the foundry and actually people on a message board know more then them. They do not want to help with these problems and are basically blowing me off.

We are currently looking for another foundry.

Thanks all for the comments.....................

 

[arunmrao]

mewhg,
I had suspected a similar situation. For business reasons or technical incapabilities,whenever situations arise this is the common ploy adopted by foundries here. Since it was a technical forum I did not discuss this aspect.

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[mewhg]

arunmrao,

Could you make an exception in this case and discuss the business aspects? This is actually very important to my company. Understanding the underlying reason behind this request from the foundry, does....in some way....relate to the technical aspect of the forum.

many thanks.........

 

[arunmrao]

mewhg,
you may contact handlename @ hotmail.com with more details.

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