Sweden - British track pieces - Origin?

I've received the following query from a German acquaintance, and wondered if any much-travelled NatPres member could help, or suggest a suitable website/forum:

"During a recent vacation in Sweden (region Berslagen) I noticed several historical rail pieces with UK markings and would be interested if there is someone (or a forum in GB) which could give me further information??

Banghammar-Kloten railway, bulit in 1877 with 100% British rail materials, dismantled in 1934, no tracks left today, just buildings.

1. There is a well preserved loading ramp with its edge made of a worn rail. I found a roll sign on this rail: RHYMNEY. Has this something to do with the former mining railway Rhymney? or is it a factory brand?
2. same place - I found in the woods a probably forgotten (useless? too heavy?) frog of a turnout. Cast markings 1888 and KW framed with a rectangle line
3. in the vicinity are rails of a slipway for small ships with rollmarkings - DARLINGTON 180x "

Thanks in anticipation,
Nick Lawrence

 

Steel rails made by Rhymney Iron Co were quite common in Sweden.
Remains still to be found in many places.
https://www.gracesguide.co.uk/Rhymney_Iron_Co