ONEDOLLAR wrote:I forget but at what temp does cast iron become pliable?
Doesn't really happen with grey iron. That's one of it's great advantages as a material for grates. You can get it up to 1000*F and it doesn't want to move...
Dcrane wrote:In theory you would think the more times you can heat up evenly cast iron grates and cool down slowly the stronger the grate would become and the place to do this would be an electric oven (because attempting it with a wood or coal fire would not heat the entire surface as "evenly"). The problem is... ive tried this with pizza ovens and it never seems to prevent the possible damage that occurs with over firing. With firebrick it well worth this investment in time (ive seen first hand how durable and long lasting and wear resistant firebrick can get if its "cured" in this fashion. Cast Iron is seemingly not that easy and if it were... manufacturers would be doing it prior to shipping. Clearly doing this with cast iron can only help (it will not hurt to be sure) but dont have high expectations for this (I've been their and done that, as im sure many have) and I could never stop warpage from an abused stove or increase the life expectancy. The solution was making a grate system that was not one piece but rather many smaller/shorter pieces that no not lay flat/horizontal but rather lay vertically (very expensive to do but proven to never fail and never require replacing).
Oddly enough I will say their IS a drastic difference between castings and foundry's, Im not so tech savoy that I can understand or know why this occurs BUT the fact is some grates made by some foundry's are vastly more durable than other grates made at other foundry's... I would say this is also the reason why antique cast iron most of time is better then new cast iron. I don't know if our forfathers used a different method of firing or cooling or if they used different mixtures in their castings but their IS a difference!
It doesn't quite work that way. You can probably heat up a grey iron casting in a home electric oven hundreds of times and it likely wouldn't do much of anything after the first few hours of cycling and that's only if there was some kind of tempering taking place. . Unless you have an oven capable of running up in the 1000*F to 2000*F range, you aren't doing much to the microstructure of grey cast iron. Of course, running in a wood or coal stove within the firepot can get up there.
I don't really know because I've never had the opportunity to study it, but from what I've seen, warpage in grates seems to come mostly from 2 separate sources: 1) the grates were either the wrong alloy or weren't stress relieved. 2) Running the grates in the stove, ash got built up on the side away from the fire. This makes the bottom of the grate notably colder than the top side of the grate that is against the fire causing thermal stresses resulting in warpage.
As far as old cast iron being better than new cast iron, I have to strongly disagree. World War II and after saw tremendous advances in our knowledge of cast irons. Grey iron metallurgy is very complex. If you want a good casting, you have to know how to specify it for the foundry to produce the alloy needed. There are many grey iron alloys...