Casting vs. Forging Material

The specs call for forgeing

I think the clue is there in black and white....unless you are the design authority then you can't change the spec'.
Find another supplier.
I get soooo annoyed as a designer if people get some 'alternative' without my approval and then wonder why it doesn't work.
Nah, whatever...make the suckers out of wood, who cares these days
Del

If a supplier is proposing an alternative, he must show that it can perform as well or better than the specification. You also need to understand the way the material will function so as to correctly assess the proposal. If you do not feel that you and your team have sufficient competence to assess these issues then you must either stick to the specification or employ someone who can assess the issues. The employment of someone competent would also be at the supplier's expense as it is not the client who is proposing the change and why should he pay for it?

Your answer is good.
But there should be a clearly defined design authority who will assess any proposal, else what happens is the supplier gives you a load of waffle 'proving' it's satisfactory, some gullible fool accepts it, problems crop up later on and the supplier says "well you signed it off"
I'm forever getting pressed into making idiotic minor changes (usually software) which I resist where possible because often the subtle reason for doing something may be difficult to recall untill it's too late....

A cautionary tale:-

Recently we had some back up batteries leaking, because I changed the trickle charging rate.
Why did I do it? Because production wanted to speed up the charge rate so they didn't have to give 'em 24 hours charge before sending them out and they pressed me to to make the change.
I should have listened to the little voice of caution in my head, but I allowed myself to be rushed into it.
Yes I screwed up big time despite being the design authority!
But if they'd just left the damn thing alone and not asked for the change I wouldn't have been given the chance to mess up.
If a spec' says something specific there is usually a damn good reason.
Del

I used to work in a plant that made ball bearings for everything, including ball valves. All were forged, some went to heat treatment for extra hardness, none were cast. You could find a different supplier or If your current supplier feels as if cast iron is going to meet or exceed the spec's, I would get an attorney to write up an "iron clad", pun intended, agreement, in which your supplier assumes all responsibility and financial liability for any failures that relate to the cast iron balls. If they won't sign, it's time to find another supplier. If they do sign, your ass is covered.

Why have a spec if you don't follow it? You remind me of the old inspector that called me down to the shop floor one day. I had written a test spec that called for no-load current to be something like 12.6 mA minimum, 27.2 mA maximum. So the inspector said, "I understand what this says, but what's the tolerance on the maximum? How much over the maximum is still OK?"

Before doing anything, I would also have the supplier refer you to other clients that are using the cast iron balls in a similar situation to yours, and get real feedback on the performance, if they don't work, you don't want to be the first one to find out.

Does any one really thinks after the feline comment at #1 further discussion is necessary?

Spec made by designer, and it says forging.

Any forging is definitely superior to cast iron strength wise and otherwise too(however not in all properties)

You are paying (spec wise) for Forging, which is much costlier than cast iron, at our area it will be atleast 3 times.

Why you want to gamble with your customer (definitely it will be used by someone else - your internal/external customer)

BTW: just for curiosity what is the process fluid, temperature and pressure and what is the forging material? Is it a code application (AWSME/API?)

Well, the Cat is smarter than most of us, so we just like to say, "Yeah, me too" and then kick the poor OP while he's down.

No! It is not OK! You cannot accept them. I'd fire you if you worked for me for even asking.

Then I'd fire purchasing for not procuring the correct material in the first place.

Are you mettalurgist engginer? If yes i believe you can make decission which one you need. Each of them has advandtage and disanvandtage. You should go to basic understanding of forging and casting, and also how is microstructure change when the material formed into desired sharp of final product. Perfect design of moulding (proper shringkage and raiser) will give better casting product. If the valve type is socket weld, I am prefer to casting due to weldability.