Is it possible to combine history data(history blocks) of 2 historians with the same set of tags to 1 historian server without Tiered setup?

As long as you don't need to include overlapping history blocks (e.g. don't need block from both servers for the same day) and this is a relatively recent Historian release (e.g. 2017 or later), this is fairly simple: copy the history blocks from one server into the other, taking care to not replace/overwrite any of the existing ones on the target server. Ideally the servers are the same Historian release, but if not, best for the target server to be the newer. 

In some cases, that is all you will need to do, but depending on the data sources and how you originally configured "server 2", it might have different "TagIDs" (the internal ID used within history blocks). If the IDs changed in the new system, you won't be able to retrieve any of that historical data without taking an extra step to match up the common tagnames with the mismatched TagIDs.

If you have that issue:

1. Copy the "C:\Historian\Data\Support\taginfo.dat" file from the same system where you copied the history blocks and place it in the most recent history block (e.g. today that is probably "C:\Historian\Data\Circular\A241217_001") on the consolidated server
2. Copy the "auto-taginfo.dat" from the same location in #1, but to the most recent auto-summary block (e.g. C:\Historian\AutoSummaryData\Circular\A241125_001" -- note, the last part of the path will most likely not be today).
3. Then, "Shutdown (and disable)..." the Historian and, once it has stopped, restart it ("Enable (allow to run)...")

If you do have overlapping blocks, it is messier: start with #1-3 above, omitting the overlapping blocks, then export the overlapping data from the source server to a CSV file and import it into the target server.