Is 'nLockTime' equal to 'lock_time' in transaction data structure?
Yes, they are the same. nLockTime is the name used in the Bitcoin Core source code (e.g. here) , whereas locktime or lock_time might be more common in JSON input/output or other pieces of software. The Bitcoin Core RPC uses locktime for example, and blockchain.info uses lock_time in its rawtx/ endpoint