How would u determine the iron content of cast iron and steel in the lab?

Being able to determine the exact content is somewhat of a tedious task; you can try speaking with the manufacturer to see what the exact molecular constituent ratios are. Otherwise a materials ysis of the alloy would be necessary; you would have to undergo methods such as silver reduction-dichromate titration, hydrogen sulfide reduction and dichromate titration, or dichromate titrimetry. Cheers