If that is the linear bearing material, the 10mm that I have appears to be case hardened which is softer steed in the centre.
There used to be a case hardening powder which was sprinkled on the red hot steel then quenched at an appropriate temp. the temp was established by colour. It requires polishing the red hot steel so the cooling colour change is apparent. It is no longer cheap
https://www.lprtoolmakers.com.au/cas...g-powder-200g/
This link may be useful
http://www.model-engineer.co.uk/foru...s.asp?th=64390