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