This was a very interesting find! I was looking for a certain blog and came across this site: astudent.wordpress.com/2007/03/29/iron-sharpens-iron
This guy has worked with metals and, as he pointed out, iron DOESN'T sharpen iron.
So what does the verse in Proverbs 27:17 mean? Iron sharpens iron; so a man sharpens the countenance of his friend. This guy pointed out that a stone or rock is needed. The Rock! It's really a very good article.