the númenorian Steel Bow (Ad."Ankalûta") was a legendary weapon of the Dúnedain.It was made of hollow steel, somewhat shorter than the average longbow.The númenorian Steel Bow became uncommon during the third Age but some adûnaic families still kept old steel bows, jealously guarded as family heirlooms.Some orcish tribes also used Steelbows instead of the more common orcish horn- or horn-composite model, but usually a much shorter variant and technically more similar to Crossbows.
speculations[]
The real-world inspiration for Tolkien´s númenórean Steelbows was most likely the Indio-Persian Steelbow.