Hi
possibly a blade from a plough (a coulter).....the first pic is of a medievel plough . The second is from the British museum and is described as .....
Iron plough coulter
Roman Britain, 1st-4th century AD
From Great Witcombe, Gloucestershire
The coulter was a technical innovation introduced to Britain by the Romans. Its function was to make a vertical cut in advance of the plough-share, which then undercut the furrow made by the coulter. This made it easier to cultivate heavy soils. Roman coulters were therefore stout knife-like iron blades with a heavy shaft by which they were secured to the plough's wooden beam.
W.H. Manning, Catalogue of the Romano-Britis (London, The British Museum Press, 1985)
Could you post a picture of the other side of the crack (shown in the first picture of your last post) as this is where I suspected the 'weld'.
Even if this is a 'coulter' .....who's to say that during war it might be utilised as a weapon.
Plough shares to swords
Best Regards David