No, a blockchain only needs one consensus algorithm/mechanism and Proof of Stake can entirely replace Proof of Work. To be precise tough: Steem uses Delegated Proof of Work which is a bit different than regular PoS. If you are interested, 
No, a blockchain only needs one consensus algorithm/mechanism and Proof of Stake can entirely replace Proof of Work. To be precise tough: Steem uses Delegated Proof of Work which is a bit different than regular PoS. If you are interested,
RE: A look into the STEEM blockchain to understand why it is awesome and successful