Killed carbon steel castings 1

[valvesarefun]

Is there any way to tell if a carbon steel casting, A216-WCB in this case, has been supplied in the fully killed condition just by looking at an MTR?

There are maximum limits in the ASTM spec for Si (0.6% max)and Mn (1.0% max), which, as I understand it, are elements used to kill steel. Is there an established minimum ammount for these elements, that will tell me if the steel has been killed or not?

 

[arunmrao]

Killing is a process of removing/reducing oxygen level in the molten metal. In the case of WCB castings, they have high levels of Si and Mn followed by addition of aluminium and calcium silicide before pouring to ensure removal of any oxygen.

Normally a good foundry practice would ensure silicon of about 0.3-0.4% and Manganese of around 0.8%. However,mechanical properties have to be satisfied,before acceptance. Hope it helps.


_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[valvesarefun]

Arunmrao,

Thank you for your reply.

Our typical casting contains Si 0.32~0.41 and Mn 0.527~0.714 (%/wt). Are these levels typically sufficient to accomplish a "full kill"? or is it a matter of Si & Mn levels plus the addition of Al and/or CaSi2 that are required to accomplish a full kill?

Also, ASTM doesnt seem to make any allowance for Al, so I'm assuming that if it is used in a WCB casting it would only be added in trace ammounts. Is this correct? My ASTM manual is really old, so my info might be out of date in respect to this question.

 

[blacksmith37]

What do you want ? Killing is typically done only with Al and/or Si. Killed steels have finer grain = better toughness. And slightly rougher surface- (only a concern for sheet steel and ERW skelp). I mean if you want a fine grain size or toughness ,specify them.
There is a level of Al ( like> 0.02% ) that is defined as "killed" but I have forgotten the exact number.

 

[arunmrao]

With such high carbon content (0.2-0.25%) and silicon, manganese content,the metal is already in a killed state. I am unable to appreciate your problem please.Why are you obsessed with the term killed steel in a treated and alloyed steel casting. You must be more concerned about its mechanical properties and gas related defects.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[valvesarefun]

Arunmrao,

It is a requirement in an end-user's valve specification that all carbon steel castings be supplied in the "fully killed" condition.

I am of the opinion that the castings provided to us are already in the killed state as you mentioned. However, our factory says that they are not killed. For some reason the factory is under the impression that they need to employ some sort of vaccum system to deoxidize/de-gas the casting, and that since their castings are poured in an "open air" foundry the castings are not killed.

I think it is a classic example of the miscommunications that arise in the global market place we all find ourselves competing in these days.

I cant really tell why the customer has put the requirement in this spec. I am assuming it is an effort to prevent porosity that could provide a leak path.

Thank you to both of you for your input on this subject.

 

[arunmrao]

valvesarefun,

The standards for ASTM A216GrWCB,does not have anywhere a mention for melt treatment. However,if you read b]ASTM A703," General requirements for pressure containing parts"[/b] along with it,this standard says that special melting techniques like vacuum melting or AOD is not a standard practice,and should be adopted,only when specifically noted against individual alloy grade(read : speciality metals) in the standard.

Thus please check with your operations and advise them accordingly.

I have once again for clarity checked through Steel Castings Handbook,however no mention is made of any further refining of melt by AOD or other techniques.

Clearly,it appears to me a case of miscommunication.

Good Luck!

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[metengr]

valvesarefun;
We procure castings SA 216 and SA 217. arunmrao is correct. If these castings are certified to meet SA 216, they are fully killed.

 

[redpicker]

valvesarefun
It sounds as if your end-user is confusing de-gassing (removing all dissolved gasses) with killing (removing dissolved oxygen). Foundry practices are not my area of expertise, and arunmrao, correct me if I am wrong, but I would think they would kill the steel as a matter of choice since trying to cast un-killed steel in sand molds would not likely lead to useable product (I am assuming these are sand castings).

In any case, if what the end-user is wanting is de-gassed steel, they should specify degassing. While degassed steels are fully killed, killed steels are not necessarily fully degassed.

rp

 

[arunmrao]

The fact that you have high levels of carbon,manganese and silicon followed by aluminium additions,indicate that the metal is fully killed. Normally this practice is considered adequate and practical for all applications.

In case of processing special metals containing high levels of Ni,Cr, ,Al and very low levels of carbon,special techniques like,AOD or vacuum refining is required.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[swall]

Valvesarefun--following up on what blacksmith37 said, maybe the customer is just looking to ensure that he has a fine grained casting. You need to have this conversation with him and see if he equates fully killed to fine grain, and if so, if there is an expected max grain size.