Albert Barnes Commentary 2 Kings 6:5

"But as one was felling a beam, the axe-head fell into the water; and he cried, and said, Alas, my master! for it was borrowed." — 2 Kings 6:5 (ASV)

The ax head - This is meant literally, as noted in the margin of some Bibles. The Jews used iron for the heads of axes from a very early date . They probably acquired knowledge of the smelting process in Egypt, where iron had been in use since at least the time of the third Rameses.