You don't seem to understand that STEEM is a completely different cryptocurrency that runs on a completely separate network and blockchain to Bitcoin.
So an address on STEEM network is completely separate from BTC network... and would likely be generated using a different private key. Likewise, the same private key would generate different keys on STEEM and BTC.
ie.
Different Networks, same Address, different private keysSTEEM: thisIsMyAddress => privkey = sOmeRandomKeyFromSteem
BTC: thisIsMyAddress => privkey = completelyDifferentBTCRandomKey
Same private key, different networks, different addressesPrivkey: thisIsMyPrivKey => Steem: someRandomSteemAddress
Privkey: thisIsMyPrivKey => BTC: completelyDifferentBTCAddress
Looking at STEEM, it seems that wallet addresses are "plaintext"... ie. I created a wallet using "FreeWallet"... and it tells me that my deposit address is "freewallet.org", and you use the Memo: "059478706001"... to deposit to my account. I suspect this means that it would gladly accept a Bitcoin address like "1bItcOInAdDrEs5"... and send the STEEM to a STEEM wallet called "1bItcOInAdDrEs5".
TL;DR - You can't send STEEM to a BTC address. You can't send BTC to a STEEM address. Your STEEM is gone, you've sent it to a STEEM address that you don't have access to.